To evaluate the usefulness of lidamidine treatment in patients with irritable colon syndrome, a controlled double blind study was carried out. Forty patients with Manning symptom criteria and negative screening to stool examination, rectosigmoidoscopy and barium enema were included. Four groups of treatment were randomly integrated: Lidamidine with and without group psychotherapy and placebo with and without group psychotherapy, for six weeks. After a washout period, treatment was switched. Thirty-eight patients with a total of 76 observations were evaluated. Favorable response was shown by 94.7% and 68.4% of those who received only lidamidine and placebo, respectively, and by 84.3% and 63.2% of those who additionally received psychotherapy. Difference with or without psychotherapy was not significant. Globally, response was better with lidamidine than with placebo (89.5% vs 65.8%, p = 0.02). Adverse reactions were minimum. Lidamidine can be a useful drug in the treatment of irritable colon syndrome.