We designed a prospective study to assess the contributing factors in puerperal breast abscess and to evaluate the treatment options. During the 4-year study period, 128 nursing women with breast infection were followed. Of these, 102 had mastitis (80%) and 26 had breast abscess (20%). Ultrasonographic examination was performed in all cases. Patient age, parity, localization of infection, cracked nipples, duration of lactation, duration of symptoms, milk culture results, breast infections during previous lactation period, treatment options, healing time, and recurrence were recorded prospectively. All mastitis patients were treated with antibiotics and none developed an abscess. Ten abscesses were aspirated, and 16 abscesses were treated by incision and drainage. Healing times were similar. There was no significant difference between mastitis and abscess groups regarding age, parity, localization of breast infection, cracked nipples, positive milk cultures, or mean lactation time. Duration of symptoms and healing were longer in cases of abscess. Multivariate analyses showed that duration of symptoms was the only independent variable for abscess development. Recurrent mastitis developed in 13 patients (10.2%) within a median of 24 weeks of follow-up. Delayed treatment of mastitis can lead to abscess formation, and it can be prevented by early antibiotic therapy. Ultrasonography is helpful for detecting abscess formation. In selected cases the abscess can be drained with needle aspiration with excellent cosmesis.