Holoprosencephaly is a birth defect affecting the medial structures of the brain and face. This investigation examined the epidemiology of holoprosencephaly in Hawaii between 1986 and 1997, using data obtained from a birth defects registry, and compared the results with those of other population-based studies. Twenty-five cases were identified, producing a prevalence of 1.09 per 10 000 livebirths. There were 17 (68.0%) livebirths, two (8.0%) fetal deaths and six (24.0%) elective terminations. Ten (58.8%) of the livebirths died before the age of 1 year. Seven (28.0%) had a known chromosomal abnormality, most often trisomy 13. Prevalence rates were higher for maternal age > 39 years, maternal race/ethnicity of Far East Asian or Filipino, females and residence in Maui County. The small number of cases limited the statistical significance of the study. However, this report confirms many of the findings from the previous studies and adds new findings, particularly the higher prevalence among Far East Asians and Filipinos.