Clindamycin colitis is being reported with increased frequency. It occurs in patients who have been taking large doses of the drug for more than ten days. It manifests as abdominal cramps associated with massive diarrhea. The plain roentgenogram of the abdomen and bariumenema study in conjunction with sigmoidoscopic and histologic examination should confirm the diagnosis. Since the disease is self-limiting, the treatment consists mainly of supprotive measures. These include maintaining electrolyte balance by administration of solutions containing salt, plasmanate and blood.