Introduction A case of pneumococcal mastitis in a breast-feeding mother 6 months postpartum is described. Mastitis is usually caused by Staphylococcus aureus . A review of the literature from 1950 to March 2018 revealed only four other cases in which the causative organism was Streptococcus pneumoniae . Case presentation The nursing mother presented with high fever and the four cardinal signs of inflammation of the left breast: calor, dolor, rubor, tumour. In milk culture Streptococcus pneumoniae was isolated in numbers exceeding 10 5 c.f.u. ml −1 . The strain was of polysaccharide serotype 11 not included in Prevnar-13. Susceptibility testing showed full sensitivity to β -lactam antibiotics as well as to macrolides, lincosamides, vancomycin and tetracycline. Conclusion Streptococcus pneumoniae should be considered as a possible causative agent of puerperal mastitis.