Ancient melanocytic nevi are benign melanocytic neoplasms that show degenerative and atypical changes, sometimes leading to a misdiagnosis of melanoma. We describe 6 patients (M:F ratio 4:2; age range, 15-84 years; median, 50 years) who presented with cellular blue nevi showing stromal changes resembling those of ancient melanocytic nevi. The lesions were located on the buttocks (4 patients) and on the trunk (2 patients) and clinically consisted of heavily pigmented nodules. Histology revealed the architectural pattern of cellular blue nevi. However, the architecture was strikingly altered by stromal changes like those seen in ancient melanocytic nevi, including increased number of large, dilated vessels with pseudoangiomatous features in 4 cases, hyaline angiopathy in 4 cases, myxoid changes, sclerosis or hyalinization of the stroma in all cases, and variable amounts of edema in 4 cases. In 2 cases, a large edematous area was present in the center of the lesion, and nests of ovoidal melanocytes and single dendritic melanocytes appeared to "float" in the stroma. Pleomorphic melanocytes were observed in all cases. Ancient blue nevi represent a morphologic variation of cellular blue nevi-Masson neuronevi with degenerative stromal changes. Recognition of these lesions can help prevent overdiagnosis of melanoma.