Introduction
Most HIV/AIDS infections in women occur at a younger age, during the first few years after sexual debut. This study was therefore designed to assess factors associated with the knowledge and utilization of the prevention of mother-to-child transmission (PMTCT) services by the teenage pregnant women when compared to mature pregnant women in Ogun state, Nigeria.

Methods
This study is an analytical cross-sectional study. A total sample of all pregnant women [52 teenagers and 148 adults] attending the primary health care centres in Sagamu local government area, Ogun State, Nigeria within a 2?months period were recruited into the study.

Results
A total of 225 respondents were recruited into the study. The overall point prevalence of HIV/AIDS infection among those that had been tested and disclosed their result was 4 [2.8%]. The prevalence of HIV among the teenagers was 2 [7.4%] compared with 2 [1.8%] among older women. Only 85 [37.8%] of all respondents were tested through the Voluntary counseling and testing (VCCT) programme and 53 (23.7%) were aware of antiretroviral therapy while 35 (15.6%) have ever used the PMTCT services before.

There was no statistically significant difference in the knowledge of the teenage pregnant women when compared with the older women about mother to child transmission (MTCT) [OR?=?1.47, C.I?=?0.57-3.95] and its prevention [OR?=?0.83, C.I?=?0.38-1.84]. The teenagers were 3 times less likely to use the services when compared with the older women. [OR?=?0.34, C.I?=?0.10-1.00]. Those from the low socio-economic background were about 6 times more likely to utilize PMTCT facilities when compared to those from high socioeconomic background [OR?=?6.01, C.I?=?1.91-19.19].

Conclusion
The study concludes that the teenage pregnant women who were more vulnerable to HIV/AIDS infection did not utilize PMTCT services as much as the older pregnant women. Special consideration should be given to teenagers and those from high socioeconomic group in the design of scale up programmes to improve the uptake of PMTCT services in Nigeria and other low income countries.