Many mental disorders show marked gender differences as regards prevalence, symptomatology, risk factors or course. Other disorders do per definition only occur in women – e.g. premenstrual dysphoric disorder (PMDD) – or are markedly influenced by female specific factors such as hormonal changes over the life cycle or during reproductive processes. Current classification systems have tried to take into account these gender aspects, but some problems will certainly have to be discussed again with the next revisions of the ICD and DSM. As regards gender differences in prevalence and symptomatology questions of gender bias in diagnostic instruments and diagnostic criteria will have to be readdressed. New findings from unselected epidemiological samples, which were analysed by gender, will have to be taken into account as well as new findings from research into gender specific personality traits, which can influence the symptomatology of mental disorders. Decisions will have to be taken whether to revise existing diagnostic criteria and provide alternative diagnostic thresholds for men and women or even to develop alternative criteria sets in certain disorders, or rather to enhance the gender neutrality of criteria. A further question to be addressed will be that of gender specific diagnoses versus diagnostic specifiers. In the whole discussion two main aims of classification should be given priority: the research aim of identifying genuine entities with a common aetiology, which means we should be able to identify specific diagnostic entities with descriptive, construct, and predictive validity quite independently of the influences of gender; and the clinical aim to improve treatment and care for men and women, which often means to offer gender-specific approaches.