A combined logistic regression and life-table analysis is presented on age-at-onset data for Huntington disease. Covariates included in the analysis were sex of the at-risk individual, parental age at onset, and sex of transmitting parent. Parental age at onset and parental sex were found to be significant covariates for age at onset in the offspring, and the appropriate logistic regression functions are calculated by maximum likelihood methods. These regression functions permit a more precise evaluation of carrier risks and likelihoods than hitherto was possible by simple computational means. We further introduce a novel method to account for sibship correlations in the significance assessment, using log-likelihood differences between different models.