Objective Gonadotropin-releasing hormone (GnRH) stimulation testing is the gold standard for distinguishing central precocious puberty (CPP) from premature thelarche (PT). Due to the limitations of this test, previous studies have elucidated the clinical and laboratory factors that predict CPP. This study explored the diagnostic importance of pelvic ultrasound in girls with CPP. Method Between May 2023 and May 2024, 55 girls with suspected CPP underwent a GnRH stimulation test and pelvic ultrasonography (PU). Additionally, bone ages were evaluated using a left wrist x-ray. Result The multivariate analysis found that basal luteinizing hormone (bLH) > 0.67 IU/L, basal follicle-stimulating hormone (FSH) > 3.5 IU/L, basal estradiol > 7.5 pg/mL, uterine volume > 2.6 cm3, and longitudinal uterine diameter >35 mm were significantly associated with a pubertal response at the GnRH test. The 2 groups had no difference in bone age and bLH/basal FSH values. Peak LH/FSH ratio had the best diagnostic performance, with an area under the curve of 0.956 (95% confidence interval, 0.864-0.993), a sensitivity of 81.82%, a specificity of 96.97%, a positive predictive value of 94.7%, and a negative predictive value of 88.9%. The optimal cutoff value was >0.59 for the LH/FSH ratio. Conclusions Uterine long axis and uterine volume measurements are noninvasive data that help distinguish CPP from PT.