Background: Undescended Testis (UDT) is the most common urogenital anomaly in male children. Its adverse effects include infertility/sub-fertility, malignant transformation, propensity for trauma/torsion and body image psychological issues. Unfortunately, only about 1-2% of male children with UDT presents at various ages for surgical intervention (orchidopexy). Aim: The aim of this study was to compare the degree of testicular atrophy index estimations from Ultrasonography, across various matched age groups in children presenting with unilateral palpable UDT and children with normally descended testes in our hospital Method: This was a prospective comparative study involving 35 male children with palpable unilateral UDT having testicular volume measurements and testicular atrophy index calculations from ultrasound and Prader wooden orchidometer, with equal number of age matched controls at University of Ilorin Teaching Hospital, Ilorin, Kwara state, Nigeria. All consented and eligible patients were stratified into two groups (I and II). Patients with unilateral palpable UDT were in group I, whilst controls who are patients with bilateral descended testes were in group II. All patients in group I subsequently had orchidopexy. The US guided testicular volume estimates using Lambert’s formulae (TV = length x width x depth x 0.71), were done for group I and II. Data were analyzed using SPSS version 23.0. P-value < 0.05 was taken as statistically significant. Result: There were 35 children in each group with median age of 3 years at presentation of patients with UDT. The mean age of the case and control were 4.5 ± 3.61 and 4.5 ± 3.96 years respectively with no statistical significance in the ages of the two groups (p = 0.960). Overall, there was progressive increase in TAI values across age groups in patients with UDT. The calculated median TAI for boys aged 6 - 9 years with US TAI for same was 28.1% (p = 0.001). The median difference in the location of the UDT within the inguinal canal during clinic evaluation was 16.5mls (p = 0.001), compared to US estimation within the inguinal canal which was 34.3mls (p = 0.887) and was not statistically significant.