Mastitis is an infection of the tissue of the breast that occurs most frequently during the time of breastfeeding. About 1%-3% of breastfeeding mothers develop mastitis. Engorgement and incomplete breast emptying can contribute to the problem and make the symptoms worse. Mastitis can occur with or without the presence of infection. As it progresses, mastitis can cause the formation of a breast abscess. Severe cases of mastitis can be fatal if left untreated. Objectives: To assess the prevalence and risk factors of mastitis in lactating females and to determine breastfeeding self-efficacy for cases of mastitis. Method: A cross sectional study in a family health unit in Sharkia governorate on women who gave birth to a healthy term infant, attending El- Aslogy family health unit for the 4th dose of child vaccine. Enrolled women have interviewed in the vaccination room for the occurrence of mastitis and its risk factors and breastfeeding self-efficacy-short form. Results: 20% of the studied lactating females developed mastitis. Three quarters of mastitis cases have no previous history of mastitis (75%), 75% suffered from nipple cracks and 70% wore bra during sleep. The mean score of Breast-feeding Self-efficacy Scale is statistically higher with non-mastitis than with mastitis (50.84 ± 8.48 versus 32.77±2.68) respectively (p<0.001). Conclusion: There is statistical significant difference between mastitis cases and female without mastitis regarding nipple cracks and breast congestion, lactating duct obstruction, wearing breast bra during sleep and using milk suction. Breast-feeding Self-efficacy Score is higher with non-mastitis than with mastitis cases. Key words: Breast feeding, Family Medicine, Nipple cracks Risk factors.