According to contemporary data Ureaplasma urealiticum and Mycoplasma hominis are considered to be the most frequently isolated causative microorganisms from the amniotic cavity. They cause intrauterine infection on preterm birth. The genital mycoplasma are detected in vaginal smears more than 25% of healthy pregnant women and the reason for their invasion towards the uterine cavity in some cases are still unknown. The aim of this study is to investigate the relation between vaginal mycoplasmal contamination and preterm birth. The observed cases are distributed into 2 groups:--patients with preterm birth--35 pregnant women,--term birth--31 pregnant women. The vaginal secretion was tested with a standard microbiological methods and with specific test mycoplasma detection and quantitative assessment. In the first group in five patients (14.3%) Ur. urealiticum was detected in association with other vaginal pathogens (bacterial vaginosis and GBS). In the term birth group 2 patients were mycoplasma positive (6.5%) and associated Enterococcus and Lactobacillus was found in them. All neonates of the mycoplasma positive mothers had sings of infection and underwent antimicrobial therapy course. The results did not demonstrate statistically significant difference in the incidence of vaginal mycoplasmal presence in preterm and term delivery but shows possible relationship between preterm birth caused by ascending mycoplasmal infection which is in association with other vaginal pathogens.