OBJECTIVE The purpose of this article is to determine the accuracy of mammography and sonography in evaluating pregnant, lactating, and postpartum women. METHODS We retrospectively reviewed diagnostic breast imaging examinations of 155 pregnant, lactating, and postpartum women with 164 lesions presenting to our breast imaging department from 2004 to 2005. Records were reviewed for clinical presentation, reported sonographic or mammographic findings with BI-RADS assessment, histologic results, and clinical outcomes. Examinations rated as BI-RADS categories 4 and 5 were considered positive. One hundred thirty-four (82%) of 164 lesions had pathology results available or longer than 12 months follow-up in our study group. Of these lesions, 12 (9%) were evaluated by mammography alone, 49 (37%) were evaluated by ultrasound alone, and 73 (54%) were evaluated by both techniques. RESULTS Of 134 lesions, 87 (65%) were in patients who presented during lactation, 34 (25%) who presented during pregnancy, and 13 (10%) who presented postpartum. The presenting symptom for 86 lesions (64%) was a palpable mass. Biopsies were performed for 40 lesions. Of these lesions, four were malignant and 36 were benign. Mammograms were dense or heterogeneously dense in 88% of patients. All four malignancies were BI-RADS category 4 or 5 according to both mammography and ultrasound. For the 85 lesions evaluated with mammography, there was 100% sensitivity, 93% specificity, 40% positive predictive value, and 100% negative predictive value. For the 122 lesions evaluated with sonography, there was 100% sensitivity, 86% specificity, 19% positive predictive value, and 100% negative predictive value. CONCLUSIONS Among lactating and pregnant women, both mammography and sonography had a negative predictive value of 100% and accurately revealed the few cancers that were present in our study group.