A two-part population-based study investigating the occurrence of infantile colic was undertaken, in which 92% of mothers with newborn healthy infants were reached. In the prospective part 152 mothers ("diary group") registered crying and fussing in their infants during 12 weeks. In the retrospective part 224 mothers ("interview group") were contacted by telephone at an infant age of 5-7 months. The colic occurrence was determined according to four different definitions; the rate varied from 3.3 to 17.1%. The classical "Wessel-type" colic was present in 9.3%. Colic defined as "crying seen as a problem by parent" was present in 12.1% of the "interview group", but in only 3.3% of the "diary group". Some earlier studies may have overestimated colic occurrence. Another possibility is an actual decline. The contributive part of preventive measures is discussed.