We performed a prospective, randomized, double-blind, placebo-controlled clinical trial of dicyclomine hydrochloride using specific diagnostic criteria for infantile colic: spells of unexplained irritability, agitation, fussiness or crying lasting greater than or equal to 3 hours/day, occurring greater than or equal to 3 days/week, and continuing for greater than or equal to 3 weeks. Dicyclomine eliminated colic in 15 of 24 (63%) infants, whereas placebo was effective in six of 24 (25%) (corrected X2 = 5.42, P = 0.02). The study also addressed the hypothesis that parental distress caused by infantile colic affects subsequent temperament and sleep patterns. The data fail to document easier temperaments or longer sleep durations at 4 months in infants whose colic ceased during treatment.