To obtain a controlled empirical description of some of the measurable clinical features of colic in a naturalistic context, 38 infants whose mothers considered crying a problem ("colic") and 38 pair-matched control infants were observed and videotaped at home 10 minutes before and after an evening feed. The parents kept a diary of infant behaviors (including crying and fussing) for 7 days following the visit. Following Wessel et al (Pediatrics. 1954;14:421-434), each "colic" infant was classified according to the number of days per week that crying and fussing duration was greater than 3 h/d. The distribution of infants with colic suggested that there were two subgroups: Wessel's colic infants, with 3 days or more per week of more than 3 hours of crying and fussing per day; and non-Wessel's colic infants, with fewer such days. Maternal measures of total daily crying/fussing duration, crying/fussing bout length, and infant temperament and objective analyses of facial activity showed a consistent pattern of differences in which Wessel's colic infants differed from both non-Wessel's colic and control infants, who in turn did not differ from each other. Both colic groups differed from control infants only in the perception of postfeed cries as being more "sick sounding." The results imply that the complaint of colic represents two (or more) groups and that there may be meaningfully distinct colic syndromes. They also provide the first independent empirical support for Wessel and colleagues' clinical distinction between "fussy" and "contented" babies.