OBJECTIVES: To report the epidemiological characteristics of isolated cleft lip, cleft palate or both (CL +/- P and CP) using population-based data in Victoria, Australia. DESIGN: Descriptive study of a cohort of children born between 1983 and 2000 notified to the Victorian Birth Defects Register by multiple ascertainment sources. PARTICIPANTS: Data were collected on patients identified with CL +/- P and CP without associated defects classified as live births, stillbirths, neonatal deaths, and terminated pregnancies < 20 weeks' gestation following prenatal identification. Information was collected on sex, plurality, maternal age, and country of birth. RESULTS: The overall prevalence (per 10,000 pregnancies) of CL +/- P was 7.8 (95% confidence interval [CI] = 7.30, 8.33; cleft lip [CL] 3.3; 95% CI = 2.97, 3.65, CL+P 4.5; 95% CI = 4.13, 4.91) and cleft palate (CP), 4.3 (95% CI = 3.89, 4.66). The prevalence of CL + P was higher among stillbirths, neonatal deaths, and terminated pregnancies than CL (without CP) and CP. Boys were at greater risk than girls for CL +/- P and girls at greater risk than boys for CP. Regardless of cleft type, there was a nonsignificant excess of clefts among singleton births than multiple births and no related effects of maternal age or country of birth. CONCLUSIONS: The prevalence of isolated CL +/- P and CP in Victoria parallels other population-based studies of the same conditions. Inclusion of stillbirths, neonatal deaths, and terminations had little impact on rates. The effect of sex and plurality on cleft type is consistent with the literature, but the effects of maternal age and country of birth remain equivocal. Further studies focusing on certain ethnic groups are warranted to explain the higher rates observed.