Background: Polycystic Ovary Syndrome (PCOS) is a common endocrine disorder with significant implications for adolescent girls' metabolic and reproductive health. While PCOS prevalence studies have been conducted across India, regional data—particularly for adolescents in Jammu—remain scarce. This study aimed to determine the prevalence of PCOS among adolescent girls in the Jammu region. Methods: A hospital-based, cross-sectional study was conducted among 100 adolescent girls at Government Medical College, Jammu. Participants were selected through multi-stage random sampling, incorporating stratification by age and socioeconomic status. PCOS diagnosis followed the Rotterdam criteria. Data collection included structured questionnaires, clinical examinations (modified Ferriman-Gallwey score for hirsutism, BMI measurements), hormonal assays, and transabdominal pelvic ultrasounds. Statistical analysis employed chi-square tests with significance set at p < 0.05. Results: The overall prevalence of PCOS was 18%. Phenotypic distribution revealed that 8% exhibited all three Rotterdam criteria, while 5% had oligo-/anovulation with signs of hyperandrogenism, 3% had hyperandrogenism with polycystic ovaries, and 2% had oligo-/anovulation with polycystic ovaries. Urban participants showed a higher prevalence (23.1%) compared to rural (8.6%). Similarly, high socioeconomic status was associated with higher PCOS prevalence (26.7%) than middle (16%) or low (10%) groups. Clinically, irregular menstrual cycles (26.7% vs. 5% regular, p = 0.012), hyperandrogenism (30% vs. 6%, p = 0.004), and family history of PCOS (30% vs. 10%, p = 0.022) were significantly associated with PCOS. Conclusion: This study found that PCOS affects nearly one-fifth of adolescent girls in Jammu, with irregular menstruation and signs of hyperandrogenism as predominant features. Urban residence and family history emerged as potential risk factors. These findings highlight the need for region-specific screening programs and early interventions to mitigate long-term health consequences. Further large-scale studies are recommended to validate these results and explore causal relationships.