Introduction: The etiology of nonpuerperal mastitis is more diverse varying from infections to autoimmune disorders. Most of them are misdiagnosed as pyogenic mastitis and are treated with routine antibiotics. In this study the various causes of nonpuerperal mastitis which required surgical intervention were evaluated. It was observed that some of the pre-malignant and malignant conditions were also presented as nonpuerperal mastitis. Materials and methods: All non-lactating women who presented with symptoms and signs of mastitis and did not respond to single course of antibiotics (active against staphylococcus) treated in tertiary care Hospital and in private practice of primary author between June 2021 to December 2022 and in those in whom the ultrasound of breast was also suggestive of inflammatory breast disease were included in the study and rest were excluded from study. The final etiological diagnosis of these patients is given by the histopathological examination of tissue taken from the wall of abscess cavity or of breast mass. Results: Total 21 patients were included in the study of which 7 patients had nonspecific infection, 3 patients were diagnosed to have tuberculous mastitis, 3 patients with idiopathic granulomatous mastitis, 2 patients with periductal mastitis, 1 patient with fat necrosis, 3 patients with atypical ductal hyperplasia and 2 patients were diagnosed to have invasive duct cell carcinoma. Conclusion: The etiology of nonpuerperal mastitis is diverse. Not only the benign conditions but premalignant conditions like ADH, DCIS and even invasive carcinoma can present with clinical symptoms and signs of inflammatory breast disease.