Little is known about the conditions of life and the specific health problems of pregnant, undocumented immigrants. This study describes the socio-demographic characteristics and health problems encountered during pregnancy among uninsured, undocumented immigrants in Geneva, Switzerland. A socio-demographic questionnaire was completed by 134 pregnant and undocumented women (mean age 27.8 years) who attended a free antenatal facility between October 2002 and October 2003. The first control of pregnancy was at a median of 10.5 weeks (range 5-33) of amenorrhoea. They were mostly Latino-American (78%), had a median 12 years of education but almost exclusively performed domestic work (91%) after an average residence in Geneva of 18 months. Half of the 62 mothers had left at least one child in their home country. One out of three had never had a cervical smear test and 13% were not immune to rubella. Unintended pregnancies (83%), mostly resulted from lack of contraception (70%). All but one delivery were simple, with a median maternity inpatient stay of 5 days (range 2-10). This population of undocumented, pregnant immigrants comprised mostly highly educated, young, Latino-American women living in poor housing conditions and wages below the legal minimum. The study identified the high proportion of unintended pregnancies as a major health issue. Future research should target these issues and programs addressing lack of access to preventive measures. As well as this, the specific needs of this hard-to-reach population, such as contraception advice, rubella vaccination and cervical cancer screening, should be supported.