Linked hospital admission data for 1968-1983 were used to identify 723 children aged 16 years or less at the time of first admission to any Scottish hospital with an ICD coded diagnosis of Crohn's disease (282) or ulcerative colitis (441). The accuracy of the coded diagnoses was checked by examination of the hospital notes of 144 patients. The coded diagnosis was incorrect in 11/83 coded as Crohn's disease and 13/61 as ulcerative colitis; frequency of incorrect coding did not change significantly with time. Despite an 18% fall in the population aged less than or equal to 16 during this time, the number of new cases of Crohn's disease rose from 10 in 1968 to 28 in 1983. Thus the recorded incidence of Crohn's disease in Scottish children has risen more than three-fold in 16 years, from 6.6 to 22.9 per million (p less than 0.0001), with no difference between the sexes. Parallel data for ulcerative colitis were rendered inaccurate by miscoding of infective gastroenteritis as colitis. In an attempt to reduce this source of error cases aged five years and under were excluded from analysis, resulting in an incidence of 19.1 cases per million aged six to 16 in 1968 and 15.6 in 1983, not a significant change (r = 0.42, p = 0.052). When males and females were analysed separately, however, there was a significant decrease in the incidence of UC in male children (r = -0.4, p = 0.028), with no change for female children (r = 0.1, p = 0.595).