The study developed: (1) a general strategy for evaluating the fit of parametric dependence models for familial clustering of ages at disease-onset; (2) a computationally simple method for genetic linkage analysis of age at onset data; (3) application and illustration of recently developed additive frailty models for complex familial dependence structures. Method (1) was applied to a family study of cardiovascular disease and a twin study of appendectomy. Method (2) was applied to ongoing genetic studies conducted at the University of California at San Francisco. Method (3) was applied to a family study of coronary heart disease in Western Australia. Well-documented, user-friendly programs were developed and made publicly available.