INTRODUCTION: Non-puerperal mastitis (NPM) is a common condition that often proves tricky to treat as it may give rise to complications and recurrences. NPM has been related to cigarette smoking through mechanisms that are not fully known. This study was aimed at analyzing the course of this patient group and at promoting guidelines for adequate treatment. MATERIAL AND METHODS: This is an audit of 178 files for patients diagnosed with NPM in 2008 at the Breast Unit at Herlev Hospital. The audit included: number of contacts, treatment, bacteriology, complications, recurrences and coding. A questionnaire was sent to all breast units in Denmark to review treatment guidelines. RESULTS: We found a large majority of smokers (73%). Non-smokers often had systemic disease or immunosuppressive conditions, and many patients had been misclassified with infections related to skin diseases. Smokers on average had 5.3 (versus 3.0 among non-smokers) outpatient visits to the unit and more than twice as many recurrences. We found quite good accordance between different breast units in Denmark in terms of treatment and follow-up regimes. CONCLUSIONS: This study confirms that NPM is a smoker's disease. Nearly all patients can be treated on an outpatient basis with no need for open incision of abscesses. We found a lack of diagnostic precision and also incorrect coding of patients with infected skin diseases or complications to surgery or radiation therapy. We find that smoking intervention should be mandatory to prevent the majority of complications and recurrences.