The aim of this study was to identify the aerobic and the anaerobic microorganisms which can be related to duct ectasia. The patients were divided into two groups. Group 1 comprised 100 patients with coloured nipple discharge (duct ectasia group), and Group 2 (the control group) was composed of 50 patients without nipple discharge. The culture media used were BHI-PRAS, blood agar, mannitol agar and MacConkey agar. There was a high frequency of bacterial growth in the two groups: 85% in Group 1 and 88% in Group 2. The most prevalent bacteria were Staphylococcus aureus and Staphylococcus epidermidis. There was a statistically significant higher rate of smokers in the duct ectasia group compared with the control group, 25 (25%) patients vs. 5 (10%), respectively (p = 0.03). These findings allow us to put forth the hypothesis that the genesis of duct ectasia may be a non-infectious inflammatory process.