Infants fulfilling the diagnostic criteria for colic will be recruited by health visitors and randomized to chiropractic treatment or no treatment. The parents will be unaware of the child's allocation. All children will be taken to the chiropractors' treatment room while the parents stay in the reception areas. Before treatment, both the recruiting health visitors and the chiropractors will note, whether they suspect musculoskeletal involvement or not. All analyses will be adjusted for known confounders, which will be recorded by the health visitor at baseline.