The fine-needle aspiration (FNA) technique is a widely used method for diagnostic assessment of breast diseases. In the current study we investigated the feasibility of sampling material for genetic studies from the same FNA samples as would be used for breast cytology. After making smears for cytological examination, the needle was rinsed into phosphate-buffered saline (PBS) solution. The material gained was sufficient for a polymerase chain reaction (PCR)-based study. As the FNA samples reflect a broad range of breast diseases, it is possible to study genetic changes at various stages of the neoplastic process. We looked for mutations in the p53 tumor suppressor gene in 198 FNA needle rinses, 42 from carcinomas and 156 from cytologically benign lesions. In the malignant samples, 22% carried mutations in the p53 gene. We also looked for p53 mutations in matching tissue sections from tumors and found the FNA needle rinses to represent the tumor well. In addition, three mutations in cytologically benign lesions were found, but none of these 3 patients were diagnosed with malignant tumors in the time frame of the study. The clinical significance of p53 mutations in benign breast tissue remains to be determined.