Craniosacral therapy (CST) or cranial osteopathy is a form of alternative medicine that uses gentle touch to feel non-existent rhythmic movements of the skull's bones and supposedly adjust the immovable joints of the skull to achieve a therapeutic result. CST is a pseudoscience and its practice has been characterized as quackery. It is based on fundamental misconceptions about the anatomy and physiology of the human skull and is promoted as a cure-all for a variety of health conditions.

Medical research has found no significant evidence that either CST or cranial osteopathy confers any health benefit, and attempts to manipulate the bones of the skull can be harmful, particularly for children or infants. The basic assumptions of CST are not true, and practitioners produce conflicting and mutually exclusive diagnoses of the same patients.

Practitioners of CST claim it is effective in treating a wide range of conditions, sometimes claiming it is a cancer cure, or a cure-all. Practitioners particularly advocate the use of CST on children. The American Cancer Society cautions that CST should never be used on children under age two. Pediatricians have expressed concern at the harm CST can cause to children and infants.

There is no evidence that CST is of use for people with autism and its use is potentially harmful. As of 2018^[update] at least two deaths had been reported resulting from CST spinal manipulation. In a small study, participants with head injuries suffered worsening symptoms as a result of CST. Additionally, if used as the sole treatment for serious health conditions, choosing CST can have serious adverse consequences; the American Cancer Society recommends those with cancer or chronic conditions should consult their doctor before starting any therapy consisting of manual manipulation.

According to the American Cancer Society, although CST may relieve the symptoms of stress or tension, "available scientific evidence does not support claims that craniosacral therapy helps in treating cancer or any other disease". Cranial osteopathy has received a similar assessment, with one 1990 paper finding there was no scientific basis for any of the practitioners' claims the paper examined.

The evidence base for CST is sparse and lacks a demonstrated biologically plausible mechanism. In the absence of rigorous, well-designed randomized controlled trials, it is a pseudoscience, and its practice quackery. Tests show that CST practitioners cannot in fact identify the purported craniosacral pulse, and different practitioners will get different results for the same patient. The idea of a craniosacral rhythm cannot be scientifically supported.

In October 2012, Edzard Ernst conducted a systematic review of randomized clinical trials of craniosacral therapy. He concluded that "the notion that CST is associated with more than non-specific effects is not based on evidence from rigorous randomised clinical trials." Commenting specifically on this conclusion, Ernst wrote on his blog that he had chosen the wording as "a polite and scientific way of saying that CST is bogus." Ernst also remarked that the quality of five of the six trials he had reviewed was "deplorably poor," a sentiment that echoed an August 2012 review that noted the "moderate methodological quality of the included studies."

Ernst criticized a 2011 systematic review performed by Jakel and von Hauenschild for including observational studies and including studies with healthy volunteers. This review concluded that the evidence base surrounding craniosacral therapy and its efficacy was sparse and composed of studies with heterogeneous design. The authors of this review stated that currently available evidence was insufficient to draw conclusions.