In developed countries much progress has been made in reducing vertical transmission of HIV using antiretroviral therapies. To achieve similar gains in Africa the acceptability of routine HIV testing of pregnant women is becoming increasingly important. Evidence of reluctance of pregnant women to undergo HIV testing has led to suggestions to offer antiretroviral therapy to pregnant women without prior HIV testing. In this study we set out to identify risk factors for preferring to avoid HIV testing among women attending an antenatal clinic in northern Tanzania in the context of a hypothetical offer of Nevirapine and to explore the issues raised in more detail in focus group discussions. Two hundred and fifty women attending an antenatal clinic in late pregnancy were interviewed. Almost half of the women preferred to be offered Nevirapine without HIV testing. In a multiple logistic model having a partner with a history of a sexually transmitted disease (OR 2.72, 95% CI 1.14-6.47, p = 0.02) and having a partner who had another sexual partner in the last year (OR 1.89, 95% CI 1.04-3.45, p = 0.04) were positively associated with a preference to avoid HIV testing; while the presence of a partner living at home or feeling able to ask their partner to go for an HIV test were negatively associated with a preference to avoid HIV testing (OR 0.46, 95% CI 0.24-0.89, p = 0.02 and OR 0.56, 95% CI 0.3-1.05, p = 0.07 respectively). FGDs (focus group discussions) suggested that the major concern of women was for the reaction of their male partners to the possibility of a positive HIV test and low confidence in the confidentiality of HIV testing. This fear may lead to low uptake of antiretroviral programmes and treatment without prior testing should be considered.