Unusual tissue changes in needle tracts after fine-needle aspiration were studied in two specimens. One specimen, a 3.0 x 2.5 cm mesenteric nodule, was found six days after a nondiagnostic transabdominal fine-needle aspiration of a retroperitoneal mass. At frozen-section examination, the nodule had proliferating spindle-shaped cells interspersed with adipocytes that raised the possibility of well-differentiated liposarcoma. On permanent sections, however, there was fat necrosis and reactive spindle-shaped cells that immunohistochemically were consistent with myofibroblasts. In the second case, a needle tract was noted in breast tissue on which a biopsy was performed two days after a cytologic diagnosis of carcinoma. The 0.4-mm-wide tract contained neutrophils, foamy histiocytes, and clumps of intact, atypical epithelial cells without a desmoplastic or elastotic component. Aside from these epithelial cells, nothing in the biopsy specimen suggested invasive carcinoma. The cells were identical to those from a comedocarcinoma present in the biopsy and mastectomy specimens. These two cases provide examples of pitfalls that may arise during the examination of biopsy specimens obtained after fine-needle aspiration.