A sudden outbreak of skin ulcers occurred in the Cook Islands beginning in early 1976. Information from the outbreak indicated that ulcers were most consistent with the clinical entity of tropical ulcer. A retrospective analysis was undertaken to determine the clinical and epidemiological features of the outbreak. The ulcers occurred most commonly in males in the 10–14 and 15–19 age groups. Antecedent trauma appeared to initiate the ulcer. Most ulcers were solitary, occurred on the lower limbs, and healed leaving a pigmented scar. The ulcers responded well to penicillin. The cause of the ulcers was not established, but gram-negative, pleomorphic bacilli were consistently observed in ulcer biopsies.