Objective: To investigate the relationship between cannabinoid receptor expression within the placenta after delivery and the problem of preterm delivery. Design, setting, and participants: The retrospective, observational study was conducted on a multicenter material of 150 women. The study group included 115 women after premature delivery. The control group consisted of 35 women after term delivery. Methods. To determine the expression of cannabinoid receptors after the end of the third stage of labour, several sections were taken from the placenta. RNA isolation, reverse transcription, and Real-Time PCR were performed to assess the expression of the cannabinoid receptors in the placenta. Results: Cannabinoid receptor type 2 expression was lower in the placentas of women after preterm delivery. Urinary tract infections and bleeding at any stage of pregnancy occurred statistically more frequently in the study group and correlated with cannabinoid receptor type 2 expression. In the study group, the history of preterm labor, history of intrauterine fetal deaths, pregnancies terminated by a Caesarean section, and uterine tenderness correlated with lower expression of cannabinoid receptor type 2 and 1a. Conclusions: Cannabinoid receptors mRNA were present in human placental tissue during pregnancy. Decreased cannabinoid receptor type 2 expression in preterm delivered placentas should be further investigated, as perinatal endocannabinoid receptor expression could serve as a predicting tool of preterm birth. For example, liquid-based cytology could be used as a noninvasive perinatal method of measuring the expression level of cannabinoid receptors in decidual cells during pregnancy. KEYWORDS: Cannabinoid receptor; CB2; endocannabinoid system; preterm delivery; PTB