Most psychiatric disorders are determined by the complex interplay between genetic and environmental factors. Aetiological research into these complex disorders raises many different questions which require a variety of statistical methods. These include survival analysis for the estimation of morbid risk, structural equation models for the partitioning of phenotypic variances and covariances into genetic and other components, complex segregation analysis to detect loci of major effect, and linkage and association analysis for the localisation and identification of susceptibility genes. Future developments in psychiatric genetics will involve the integration of genetic and epidemiological statistics in order to study the interplay between genetic and environmental factors in the complex pathways which lead to mental disorders.