Background: Some malformations are clearly associated with older maternal age, but the effect of older age of the father is less certain. The aim of this study is to determine the degree to which maternal age and paternal age independently influence the risk of having a child with oral clefts. Methods: Among the 1,489,014 live births in Denmark during 1973-1996, there were 1920 children with nonsyndromic cleft lip with or without cleft palate and 956 children with nonsyndromic cleft palate. We used logistic regression to assess the impact of parental age on the occurrence of cleft lip with or without cleft palate and cleft palate. Interaction between mother's and father's age was included in the analysis. Results: Separate analyses of mother's and father's age showed that older age was associated with increased risk of both cleft lip with or without cleft palate and cleft palate only. In a joint analysis, both maternal and paternal ages were associated with the risk of cleft lip with or without cleft palate, but the contribution of each was dependent on the age of the other parent. In the analysis of cleft palate only, the effect of maternal age disappeared, leaving only paternal age as a risk factor. Conclusion: Both high maternal age and high paternal age were associated with cleft lip with or without cleft palate. Higher paternal age but not maternal age increased the risk of cleft palate only.