Eleven cases of neonatal mastitis diagnosed at National Taipei College of Nursing Health Center, since 1983, have been reviewed by chart retrospectively. All 11 cases occurred in full-term infants 1-4 weeks postnatally. Female predominated with male: female ratio of 1: 1.75. The mastitis of these cases were confined to unilateral side and did not spread systemically. Gram stain smear of the purulent material got from aspiration, incision or spontaneous rupture of abscess were attempted in ten cases and Gram positive cocci were observed in nine of whom pus culture yield staphylococcus aureus later in eight. We feel Gram stain is one of the rapid and useful diagnostic method. Treatment was given by appropriate antibiotics parenterally followed by surgical incision or drainage when fluctuation was present. The prognosis of neonatal mastitis is excellent. In general, these our clinical observation are similar to those described in the literatures since 1950s.