Aggregates of cells resembling those of cutaneous nevi have been found in the capsules of lymph nodes. Although seemingly rare, this extraordinary lesion could conceivably occur often enough to be more than a pathological curiosity, and should be differentiated from metastatic tumor. Slides from every axillary lymph node dissection for female mammary carcinoma in the years 1964 and 1974 at Memorial Hospital were reviewed, as were slides from 100 consecutive lymph node dissections performed during 1974 in patients with malignant melanoma. Nevus cell aggregates (NCA) were associated with three of 17,504 lymph nodes (0.017%) obtained from 909 mastectomies, or 0.33% of the cases. Among the 100 lymph node dissections for malignant melanoma, NCA were found associated with three of the 2,607 lymph nodes examined (0.12%), or 3.0% of the cases studied. Since NCA occur in association with lymph nodes more often than previously thought, the possibility that they may be a potential source of malignant melanoma in patients without a demonstrable cutaneous or mucosal primary is discussed.