The 1998 Stanley Cup playoffs, the playoff tournament of the National Hockey League (NHL), began on April 22, 1998 following the 1997–98 regular season. The sixteen teams that qualified, eight from each conference, played best-of-7 series for conference quarterfinals, semifinals and championships, and then the conference champions played a best-of-7 series for the Stanley Cup.

The playoffs concluded on June 16 with the Detroit Red Wings defeating the Washington Capitals in a four-game sweep to win their second Stanley Cup championship in a row. Red Wings captain Steve Yzerman was named playoff MVP, and awarded the Conn Smythe Trophy. The 1997–98 Detroit Red Wings were the last team to defend their Stanley Cup title until the Pittsburgh Penguins successfully defended their Stanley Cup title in 2017.

In the Eastern Semis, the Buffalo Sabres made history as they became the first team in NHL history to complete a four-game sweep of the Montreal Canadiens on Montreal ice.

For the first time since 1969, the Chicago Blackhawks missed the playoffs, ending the second-longest active playoff appearance streak in NHL history at 28 seasons. The longest active appearanced streak moved to the St. Louis Blues at 19 consecutive seasons. Also, both the Islanders and Rangers missed the playoffs in the same season for the first time.

The top eight teams in each conference qualified for the playoffs. The top two seeds in each conference were awarded to the division winners; while the six remaining spots were awarded to the highest finishers in their respective conferences.

The following teams qualified for the playoffs:

In each round, teams competed in a best-of-seven series, following a 2–2–1–1–1 format (scores in the bracket indicate the number of games won in each best-of-seven series). The team with home ice advantage played at home for games one and two (and games five and seven, if necessary), and the other team played at home for games three and four (and game six, if necessary). For any series played between Central and Pacific Division teams, the team with home ice advantage had the option of using a 2–3–2 format to reduce travel, with the sites for games five and six switched; if the 2–3–2 format was chosen, the team with home ice advantage then had the additional option to start the series on the road instead of at home. The top eight teams in each conference made the playoffs, with the two division winners seeded 1–2 based on regular season record, and the six remaining teams seeded 3–8.

The NHL used "re-seeding" instead of a fixed bracket playoff system. During the first three rounds, the highest remaining seed in each conference was matched against the lowest remaining seed, the second-highest remaining seed played the second-lowest remaining seed, and so forth. The higher-seeded team was awarded home ice advantage. The two conference winners then advanced to the Stanley Cup Finals, where home ice advantage was awarded to the team that had the better regular season record.