Infertility, defined as the inability to conceive after one year of regular unprotected intercourse, affects millions of couples worldwide, with prevalence rates varying across developed and developing nations. The main objective of the study is to find the association between low BMI and anovulation with primary infertility in women of reproductive age. This cross-sectional study was conducted in Khyber Teaching Hospital Peshawar from January 2023 to December 2023. A total of 340 female participants were added using convenient sampling methods. Data collection consisted of comprehensive clinical evaluations, including anthropometric measurements to assess BMI, hormonal assays to determine ovulatory status and detailed reproductive histories. BMI was calculated as weight in kilograms divided by height in meters squared (kg/m^2), with participants categorized into low BMI (BMI < 18.5 kg/m^2) and normal BMI (BMI ≥ 18.5 kg/m^2) groups. Data were collected from 340 female participants. The mean age was 28.5± 4.2 years for those with low BMI and 30.1± 3.8 years for those with normal BMI. Among underweight individuals, 50 were classified as infertile and 20 as fertile, totaling 70 participants. Of normal-weight individuals, 40 were infertile, and 120 were fertile, totaling 160 participants. In the overweight group, 30 were barren, and 50 were fertile, totaling 80 participants. Low BMI showed a significantly increased adjusted odds ratio (AOR) of 3.00 (95% CI: 1.80 - 5.00, p < 0.001) for infertility. Age, socioeconomic status, smoking, and alcohol consumption did not show significant associations with infertility. It is concluded that low BMI is significantly associated with an increased risk of anovulation and primary infertility in women of reproductive age, even after accounting for potential confounders.