BACKGROUND: Previous research suggests that ethnic self-identity has little consequence for objective health outcomes compared to the structural dimensions of ethnicity. METHODS: Using qualitative data, we investigated perceptions of ethnicity in relation to health among Luo men in the slums of Nairobi, Kenya. RESULTS: While recognizing the complicated cultural origin of poor health, responding Luo men stressed on gender and everyday livelihood situations as being more critical for their health than Luo customs. Recognition of the structural causes of ill-health among the men overlapped with lay notions derived from particular expressions of Luo culture in urban slum contexts. To some extent, respondents regarded the performance of their sense of ethnic identity as protective, though they also admitted to the health-damaging repercussions of some of the ways they enacted aspects of Luo culture. CONCLUSION: Ethnic beliefs that link particular enactments of local customs with health outcomes may motivate the performance of cultural identity in ways that can produce critical health outcomes.