"Basket Case" is a song by the American rock band Green Day, released on August 1, 1994, by Reprise Records as the second single from the band's third studio album, Dookie (1994). The song spent five weeks at the top of the US Billboard Alternative Songs chart and garnered a Grammy Award nomination in the category for Best Rock Vocal Performance by a Duo or Group. Its music video was directed by Mark Kohr and filmed in an abandoned mental institution in California. In 2001, the song appeared on their greatest hits album International Superhits!. In 2021, "Basket Case" was ranked number 150 in Rolling Stone's updated list of the "500 Greatest Songs of All Time".

Armstrong revealed in a 2024 podcast interview that around 1992–93, while living with bandmates, he wrote an early version of the song as a love song using a four-track recorder. He wrote the lyrics while on crystal meth, thinking he "was writing the greatest song ever" but finding them "embarrassingly bad" once sober. He set the song aside before eventually returning to rewrite the lyrics around his experiences with panic attacks, saying this was "the best decision I'd ever made, probably, as a songwriter". The band subsequently demoed the rewritten song at Andy Ernst's Art of Ears studio in San Francisco.

"Basket Case" was one of the songs producer Rob Cavallo heard when he received Green Day's demo tape. He ended up signing the band to Reprise Records in mid-1993. Green Day and Cavallo recorded the version of "Basket Case" released on the trio's major label debut Dookie between September and October 1993 at Fantasy Studios in Berkeley, California.

"Basket Case" is a punk rock and pop-punk song, performed in the key of E-flat major. Fred Thomas of AllMusic described the track as a "neurotic punk rock cardio workout". The introductory verse features only Armstrong and his guitar. Towards the end of the first chorus, the rest of the band joins in, with Tré Cool adding fast tom fills and explosive transitions and Mike Dirnt adding a bass line that is reminiscent of the vocal melody. The song's chord progression closely mirrors that of Pachelbel's Canon.

In the song's second verse, the lyrics reference soliciting a male prostitute. Armstrong explained: "I wanted to challenge myself and whoever the listener might be. It's also looking at the world and saying, 'It's not as black and white as you think. This isn't your grandfather's prostitute – or maybe it was.'"

"Basket Case" was the second single released from Dookie, following "Longview". It peaked at number one on the Billboard Modern Rock Tracks chart, a position it maintained for five weeks. In 1995, the song garnered a Grammy Award nomination in the Best Rock Vocal Performance by a Duo or Group category.

In his weekly UK chart commentary, James Masterton wrote, "Something of an instant classic [...] it is certainly one of the most alternative Top 10 smash since Radiohead's 'Creep'. As to where it goes next it is hard to tell but it could potentially open the door for a flood of the post-Nirvana young American rock bands who are currently making waves on the other side of the Atlantic." Andrew Mueller from Melody Maker commented, "Green Day themselves are an enthusiastically rockin' kind of act who've learnt a neat trick or two from The Buzzcocks and The Ramones and are the sort of band I'm regrettably likely to think are the future of rock'n'roll if I've drunk enough to stun an ox." Music Week gave the song three out of five, describing it as "the Generation X-flag-wavers' splenetic slice of Bay Area punk". John Mulvey from NME wrote, "Long-time heroes of the US skatepunk scene. Green Day are These Animal Men without the crap Brit-mod trappings and with slightly better songs. Bouncy, a bit fraggly and a bit annoying, but there are worse things in the world. Like 'Speed King', for starters."

Upon the re-release, another NME editor, Andy Richardson, praised it as "an irresistible punk snort, a ripping three-minute blast or the ultimate good mood record to play before you go out, depending which way you look at it." Paul Evans from Rolling Stone declared it as a "rave-up", noting that Green Day's lyrics "score graffiti hits". Mark Sutherland from Smash Hits gave it a top score of five out of five and named it Best New Single. He wrote, "Their last single 'Welcome to Paradise' grazed the top 20 here but this is the one to make your mum hammer on your bedroom door 'cos it sounds like you're smashing up your wardrobe. And the funny thing is — you will be 'cos it's quite the most fantastic bedroom-trashing anthem in too long a while." Charles Aaron from Spin ranked "Basket Case" number 19 in his list of the "Top 20 Singles of the Year" in December 1994. Troy J. Augusto from Variety described it as "psycho-rave".