Background: Primary malignant lymphoma of the thyroid accounts for <5% of all thyroid malignancies and is primarily treated with chemotherapy and external beam radiation. With the advent of modern immunophenotypic analyses, fine-needle aspiration (FNA) can potentially obviate the need for surgical procedures. Methods: To investigate the utility of FNA, data from 23 consecutive patients with primary malignant thyroid lymphoma evaluated at the Johns Hopkins Hospital from July 1985 to April 2000 were analyzed. Results: Patients were categorized into two groups: those diagnosed before 1993 (group 1, n = 12) and those diagnosed after 1993 (group 2, n = 11). Although patients in group 1 were slightly older, there were no other differences between the groups with regard to sex, tumor grade, or tumor stage. Although no patient in group 1 was successfully diagnosed by FNA alone, seven patients (63%) in group 2 were diagnosed solely by FNA (P = .019, χ2 analysis). Therefore, all 12 patients in group 1, but only 4 of 11 patients in group 2, required open surgical biopsy. Conclusions: Primary thyroid lymphoma is an uncommon malignancy usually treated nonsurgically once the diagnosis is established. In most patients with malignant lymphoma of the thyroid, FNA, should obviate the need for open surgical biopsy.