Persistent nipple pain in lactating women, burning in nature, and associated with radiating breast pain, has been claimed by some authorities to be due to 'thrush' (candida) infection. Yet, scientific proof has been lacking. This study compared microbiological assessment of 61 women with nipple pain, 64 women without nipple pain, and 31 non-lactating women. Swabs of the nipple and baby's mouth, and expressed breast milk were collected for culture. Growth of Candida albicans (nipple and milk) was found more often in the women with nipple pain (19%) than in the control group (3%, p < 0.01). In addition, Staphylococcus aureus was also associated with nipple pain (p < 0.0001), and independently associated with nipple fissures (p < 0.0001). Neither C. albicans nor S. aureus was found on the nipples of the non-lactating group.