Colchicine is a widely used treatment for Behçet's syndrome, even though in a previous 6-month controlled study, it was shown to be effective only in controlling erythema nodosum and arthralgias. We reassessed the effect of colchicine in Behçet's syndrome in a study conducted among a larger group of patients for 2 years. We randomized 116 patients with Behçet's syndrome (60 male/56 female), who had active mucocutaneous disease without eye or major organ involvement, to receive either placebo or colchicine (1-2 mg/day, adjusted to body weight) in a double-blind trial for 2 years. The primary outcome measure was the sustained absence of any lesions during treatment (complete response). The secondary outcome measure was the difference in the number of mucocutaneous lesions or arthritic joints between the active drug and placebo arms. Women and men were analyzed separately. Eighty-four patients (72%; 45 male, 39 female) completed the 24-month study. Kaplan-Meier analyses showed significantly more complete responses in the colchicine treatment group in terms of reduced occurrence of genital ulcers (P = 0.004), erythema nodosum (P = 0.004), and arthritis (P = 0.033) among the women, and reduced occurrence of arthritis (P = 0.012) among the men. The mean numbers of genital ulcers (P = 0.001), erythema nodosum lesions (P = 0.002), and arthritic joints (P = 0.014) among the women were less in the colchicine group, and the mean number of arthritic joints (P = 0.026) among the men was less in the colchicine group. Adverse effects were similar in both groups. Colchicine may be useful for treating some of the manifestations of Behçet's syndrome, especially among women. This might be a reflection of less severe disease among the women.