Background: Knowledge concerning the value of menstrual cycle observation and its use to monitor reproductive health is underestimated and limited in women’s health promotion, education and health care. The American College of Obstetricians and Gynecologists and the Academy of Pediatrics recommend that observations of a developing cycle should start as early as during puberty in order to pre-screen girls for the risk of fertility disorders such as polycystic ovar y syndrome. With numerous reports of fertility issues on the rise, such a simple tool as self-observation of the menstrual cycle becomes particularly useful as it provides an insight into the natural rhythm of fertility and, in the case of abnormalities, i.e. any deviations from its normal course, reduces the time until the first medical consultation. In Poland, there are several non-governmental and non-profit organisations which, through certified teachers of fertility awareness methods, can professionally support the educational process of adolescents and adults as well as health care professionals in the field of fertility awareness, health education, and natural family planning. Aim: The aim of the presented study was to analyse 105 menstrual cycle observation sheets among Polish women who did not use contraception in accordance with the principles of the symptothermal double-check method. Method: The study was performed using the documentation analysis method, with 105 menstrual cycle observation sheets and the SPSS Statistics software suite, version 25. The level considered statistically significant was p < 0.05. Results: The average age of the studied women was 29 years. The majority of them, i.e. more than 58%, were unmarried and childless (79.1%). The average length of the menstrual cycle was 28.6 days. The average duration of the luteal phase was nearly 13 days. The average number of days of highly fertile mucus was nearly 4 days. The average length of cycles in women over 35 years of age was 28.88 days, while in women under 35 years of age 28.48 days. The age of onset of the first menstrual period ranged between 10 and 17 years of age. Conclusions: The studied group of women was homogeneous in terms of the adopted eligibility criteria, i.e. they had typical cycles and did not use contraceptive methods. The examined parameters of the menstrual cycle – the average length of the cycle, the course of the luteal phase, and the average duration of highly fertile mucus – satisfied the criteria of a normal cycle according to the symptothermal double-check method.