A short review is given of some of the adverse reactions to prostaglandin synthetase inhibitors. Broadly, these sideeffects can be divided into those common to the whole group, and those more or less characteristic of the individual drugs. Among the former, symptoms from the gastrointestinal tract and from the central nervous system are the most conspicuous. Skin reactions, bronchospasm, and serious blood dyscrasias have been reported for several of these drugs and the list of more rare sideeffects is long. It is concluded that drugs like phenylbutazone and oxyphenbutazone should not be used for treatment of dysmenorrhea because of the risks of serious adverse reactions. However, even if among the newly introduced compounds none can be said to be free from risks, some seem to have an acceptable ratio between therapeutic efficacy and sideeffects.