Studying a large series of malignant lymphoma is important to increasing our understanding of this disease. Based on the World Health Organization classification system, 1983 cases of lymphoma at Siriraj Hospital were classified as either non-Hodgkin lymphoma (NHL) (92.1%) or Hodgkin lymphoma (HL) (7.9%). The NHL cases were 75% B cell type and 25% T cell type. Diffuse large B-cell lymphoma, unspecified peripheral T-cell lymphoma, follicular lymphoma, extranodal marginal zone B-cell lymphoma, precursor T lymphoblastic lymphoma, and Burkitt lymphoma accounted for 84.3% of all NHL cases found. Mixed cellularity and nodular sclerosis types constituted 77.7% of the HL cases found. An overall male preponderance was observed, but sex distribution differed among various types of lymphoma, and a female preponderance was observed in the elderly subjects. Changes in the frequency of B-cell NHL by age were characteristic: <50% in the first decade of life, a further decrease in the second decade, >60% in the third decade, and increases thereafter, reaching 90% after the seventh decade. High frequency of follicular lymphoma in Bangkok but low frequency in the Northeastern region and high frequency of HL in the Southern region were significant (P <0.05). Extranodal involvement was observed in 58.7% of NHLs, commonly affecting the upper aerodigestive tract and gastrointestinal tract, with some differences in geographical distribution. Higher frequencies of T-cell NHLs involving extranodal sites and of B-cell NHLs involving lymph nodes were significant (P <0.05). The distribution of various types of lymphoma and comparison with other large series of lymphoma further demonstrates the heterogeneity of this disease.