Objective The aim of the present study was to determine if the favourable cardiopulmonary and metabolic benefits induced by exercise training (ET) programme are maintained after its cessation. Patients Thirty-two young overweight polycystic ovary syndrome (PCOS) women matched for age and body mass index (BMI) with other 32 PCOS patients was enrolled. The first group [PCOS-T (trained)] underwent 24-week ET programme, whereas the second [PCOS-DT (detrained)] underwent 12-week ET programme followed by 12-week detraining period. Methods At baseline, after 12- and 24-week follow-up, all PCOS women were studied for their hormonal (ovarian and adrenal androgens), metabolic (glucose and insulin) and lipid profile, and underwent cardiopulmonary exercise test. Results After the initial 12-week ET programme, both PCOS-T and PCOS-DT groups, without differences between groups, showed a similar significant ( P < 0·05) improvement in BMI, fasting insulin, areas under curve insulin (AUC INS ), glucose and insulin AUC (AUC GLU/INS ), high-density lipoprotein-cholesterol (HDL-C), low-density lipoprotein-cholesterol (LDL-C) and maximal oxygen consumption at cardiopulmonary exercise test (VO 2max ). At 24-week follow-up, PCOS-T group showed a significant ( P < 0·05) improvement in BMI, fasting insulin, AUC INS , AUC GLU/INS , LDL-C, HDL-C and VO 2max , in comparison to baseline and 12-week follow-up. At same follow-up visit, the all parameters resulted significantly ( P < 0·05) worsened in PCOS-DT group in comparison to 12-week follow-up and PCOS-T group. In PCOS-DT group, no parameter assessed at 24-week follow-up was significantly different in comparison with baseline. Conclusion In young PCOS women, 12-week detraining resulted in a complete loss of the favourable adaptations obtained after ET.