Epidemiological reports on lymphomas often begin, and sometimes end, by stating that little is known about the causes of the condition(s) under study. This is slowly changing as information on the pathological diversity of subtypes accumulates. This review examines the epidemiology of lymphomas, focusing on the impact of the latest World Health Organization (WHO) classification. Use of appropriate disease classifications is critical to the research process, but many studies conducted in previous decades have been hampered by the need to aggregate data into the broad lymphoma groupings of Hodgkin and non-Hodgkin, either because primary source information was recorded in that way, or because diagnostic standards were inconsistently applied. Population-based data on age and gender are presented using the latest WHO classification, revealing considerable subtype heterogeneity. Aetiological factors highlighted include the unexplained male bias that is strikingly evident for many subtypes across all ages, and the relationship with autoimmune disease, which, although often associated with increased lymphoma risk, is generally more common in females. This is an exciting time for epidemiological research into haematological malignancies, where the application of modern disease classifications is beginning to discriminate between subtypes revealing features that future aetiological hypotheses should seek to address.