We sought to evaluate the effects of oral testosterone undecanoate treatment based on the temporary growth of penis and the complications of surgery in children with microphallic hypospadias. A total of 72 randomized consecutive children with microphallic hypospadias were included in the study from March 2011 to September 2013. While 34 children were treated with oral testosterone undecanoate treatment prior to surgery on time (group 1), 36 children did not receive any treatment preoperatively (group 2). All children underwent hypospadias repair using transverse preputial island flap (Duckett technique) urethroplasty or combination of Duckett and Thiersch-Duplay techniques. Penile length, diameter, serum testosterone level, and secondary effects were recorded before and after therapy in group 1. Postoperative complications were assessed with respect to fistulas, urethral strictures, diverticula, meatal stenosis, and glanular dehiscence in both groups. Mean penile length and diameter increased significantly by 1.06 +/- A 0.53 cm (P < 0.05) and 0.30 +/- A 0.09 cm (P < 0.05). Postoperative complications included urethrocutaneous fistulas in nine patients (25 %) in group 2 compared to two patients (5.9 %) in group 1 (P < 0.05). While three patients (8.3 %) in group 2 had urethral strictures, no patient in the testosterone group had this complication (P > 0.05). There were three patients (8.3 %) with diverticula in group 2 and three patients (8.9 %) with this complication in group 1 (P > 0.05). None of our patients had signs or symptoms of meatal stenosis, glanular dehiscence, or residual chordee in both groups. Finally, there was a significant difference between the overall reoperation rates of group 2 (14 patients, 38.9 %) and group 1 (five patients, 14.7 %, P < 0.05). Pretreatment with oral testosterone undecanoate was effective in improving the temporary penile growth and decreasing the surgical complications in children with microphallic hypospadias.