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Epidemiologic evidence suggests a seasonal pattern in the occurrence of Hodgkin lymphoma (HL), with an incidence peak around the month of March. This pattern may reflect seasonal variation in the prevalence of an infectious agent involved in HL development. Using Poisson regression, we examined monthly variation in HL diagnosis in Sweden between 1958 and 1998, based on data from the population-based Swedish Cancer Registry. Older adults (50 to 79 years) were marginally more likely to be diagnosed in February, but there was no monthly variation after stratifying by sex. Young adult males (15 to 49 years) presented more often in February, whereas young adult females presented less often in August and December. Among children (<15 years), boys were significantly more likely to have been diagnosed in March, whereas there was no seasonal incidence pattern among girls. The seasonal pattern in HL diagnosis among young adults and boys is consistent with an infectious origin, whereas the results among older adults neither support nor dispute the possibility of an infectious etiology in this age group. © 2005 Wiley-Liss, Inc.