The pathologic evaluation of microscopic slides from patients with possible HD or NHL must be performed in the context of complete chronology of the patient's history. Advances in flow cytometry (S-phase analysis), immunophenotyping, and molecular genetics may be of value in diagnosis, classification, and prognostication. The Rye modification of the Lukes-Butler classification of HD has been stable since 1966 and is widely accepted because of its proven reliability. By contrast, the proliferation of classifications of NHL since 1966 speaks for imperfection, partially due to the still incomplete understanding of this diverse group of lymphoreticular malignancies. Successive classifications have incorporated immunologic relationships and concepts and added a clinically significant grading system. A goal of the working formulation was to allow translatability between classifications in the interest of comparison and communication of clinical and research results. Knowledge of the patterns of involvement and spread by HD and by the different categories of NHL helps to narrow the differential diagnosis of radiologic findings. An awareness of the benign, reactive processes and nonlymphoreticular malignant neoplasms that mimic HD and NHL is essential to avoiding misdiagnosis.