Although the topic is somewhat contentious, fine-needle aspiration (FNA) is frequently used in conjunction with flow cytometry (FC) to evaluate lymphoid proliferations. Despite the fact that the FNA and FC are often analyzed independently, no previous large-scale study has independently analyzed FC of FNA specimens. FC reports of 511 FNAs were retrospectively reviewed and FC diagnoses categorized as monoclonal, atypical, normal/reactive, or insufficient cellularity (3.9%). Abnormal immunophenotype was considered a positive test result. "Gold standard" diagnoses were established by histologic examination, treatment based on FNA, or clinical features. In 92.2% (451/489), there was adequate follow-up. The diagnostic accuracy of FC was 88.4%, sensitivity was 85.8%, and specificity was 92.9%. In addition, FC accuracy for classes of non-Hodgkin lymphoma was assessed. We conclude that FC is an independently accurate ancillary test in the evaluation of FNA. However, the presence of false-negative and false-positive cases supports the common practice of correlating FC with cytomorphologic findings even if performed independently.