The aims of the study were to ascertain whether patients have similar a fertility rate to the background population in Leicestershire and whether they have a similar rate of congenital malformations compared to the background population in Leicestershire. Over 1400 patients were invided to participate with an overall response rate of 81% after three successive mailings. The response rate was similar for both sexes and between the disease groups. The crude infertility rate for the group was 21%. The mean number of children for the whole group was 1.7 +/- 1.3 but both men and women with Crohn's disease had significantly less children than would be expected, (men with Crohn's disease 1.5, women with Crohn's disease 1.2). There were 39 children (2% of overall births) with congenital abnormalities reported by patients with inflammatory bowel disease and in 29 cases the parents reported taking sulphasalazine (Table 3). Although this figure compares well with the 1.8% reported congenital abnormality rate for Leicestershire within the patient group in this study congenital malformations were significantly related to sulphasalazine use, z = 4.3, P < 0.0001. In conclusion sulphasalazine not only as causes morphological abnormalities in spermatozoa but may increase the chances of having congenitally abnormal offspring amongst men with IBD. The effects of other 5-aminosalacylic acids have yet to be studied in detail.