Context: Women with polycystic ovary syndrome (PCOS) have an increased risk of metabolic syndrome (MetS). Both PCOS and MetS are associated with excess weight. Objective: To examine the effect of a three-component lifestyle intervention (LSI) with or without short message service (SMS+ or SMS−, respectively) on the prevalence and severity of MetS and metabolic parameters, compared to care as usual (CAU). Design: Randomized controlled trial. Methods: Women diagnosed with PCOS and a BMI >25 kg/m2 (n = 183) were either assigned to a 1-year three-component (cognitive behavioural therapy, diet, and exercise) LSI, with or without SMS support, or to CAU which provided weight-loss advice only. Main outcome measures included changes in the prevalence of MetS, the continuous MetS severity z-score (cMetS z-score), metabolic parameters, and the impact of weight loss. Results: After 1 year, the decrease in the cMetS z-score was greater in the SMS+ group than the CAU group (−0.39, P = 0.015). The prevalence of MetS changed with −21.6% (P = 0.037), −16.5% (P = 0.190), and +7.0% (P = 0.509) in both LSI groups and CAU group, respectively. A post hoc analysis for both LSI groups combined vs CAU resulted in a MetS difference of −25.9% (P = 0.046). Moreover, weight loss per se resulted in significantly favourable effects on all metabolic parameters. Conclusions: This three-component LSI was more successful in improving metabolic health compared to CAU. Therefore, we recommend this intervention to women with PCOS and excess weight, provided that a clinically relevant weight loss is being pursued.