Homeopathic aggravations have often been described anecdotally. However, few attempts have been made to scientifically verify their existence. This systematic review aimed at comparing the frequency of homeopathic aggravations in the placebo and verum groups of double-blind, randomised clinical trials. Eight independent literature searches were carried out to identify all such trials mentioning either adverse effects or aggravations. All studies thus found were validated and data were extracted by both authors. Twenty-four trials could be included. The average number of aggravations was low. In total, 50 aggravations were attributed to patients treated with placebo and 63 to patients treated with homoeopathically diluted remedies. We conclude that this systematic review does not provide clear evidence that the phenomenon of homeopathic aggravations exists.