This study evaluates the mammographic findings in 352 patients, aged 30-85 years, who underwent spot localization and biopsy for evaluation of nonpalpable breast abnormalities. Malignancy was found at biopsy in 114 cases. The mammographic appearance (specifically, whether grouped microcalcifications, mass, or both were present) was correlated with patient age and histologic findings (specifically, whether the pathologic changes were infiltrating or noninfiltrating in nature). The prevalence of malignant conditions increased directly with age. The presence of grouped microcalcifications as the sole indicator of malignancy was seen in 100% (seven of seven) of the patients in the 30-39-year age group, 64% (18 of 28) in the 40-49-year age group, 37% (11 of 30) in the 50-59-year age group, 30% (seven of 23) in the 60-69-year age group, and 23% (six of 26) in the 70-85-year age group. Of the 49 tumors that were manifested solely as microcalcifications, 34 (69%) were noninfiltrating. The finding of grouped microcalcifications should be aggressively investigated, since it may indicate noninfiltrating carcinoma in an early stage, when the potential for cure is greatest.