All newly diagnosed cases of Hirschsprung's Disease among children born in Baltimore City and County, Maryland and diagnosed within the Baltimore Standard Metropolitan Area during 1969 through 1977 were identified. Using hospital records and death certificates, 33 cases were ascertained. An overall incidence rate of 18.6 per 100 000 livebirths was found, similar to that reported by others. A high male to female ratio (4.32:1) was found; the ratio for non-whites to whites was 1.67:1. Non-white males had the highest rate, 37.6 per 100 000 livebirths. These findings plus the fact that 9% of these children were also diagnosed as having Down's Syndrome, were evidence that the aetiology of Hirschsprung's Disease may be partially genetic. Among environmental factors studied, there was no time trend and no relationship with socioeconomic status found. Among whites, there was a larger percentage of children who were the first births of mothers aged 30 and above, a result previously reported for children with neural tube defects. Very little is known about micro-environmental factors in relation to Hirschsprung's Disease and this would seem to be the area for future emphasis in research.