Purpose To compare the androgen receptor (AR) status of the appendix testis (AT) in congenital undescended and retractile testes. Materials and methods Twenty-four appendix testes (AT) were removed from 21 boys to detect AR expression by immunohistochemistry and immunofluorescence staining. Group 1 ( n  = 3) includes ATs from three patients with unilateral and group 2 ( n  = 6) with bilateral congenital undescended testis. All patients with bilateral form had been previously treated with human chorionic gonadotropin (hCG) without an acceptable effect. Group 3 ( n  = 12) includes ATs collected from 12 boys with acquired undescended testis or retractile testicle. Group 4 ( n  = 3) includes ATs from three young adults who received hCG treatment for undescended testis in their childhood and underwent open testicular biopsy to investigate infertility. Further seven ATs were collected to detect AR mRNA using RT-PCR analysis. Results Both immunohistochemistry and immunofluorescence staining of ATs showed AR expression in 100 % of the cases in groups 3 and 4 (12/12 and 3/3), but there was no visible AR expression in groups 1 and 2 (0/3 and 0/6); however, RT-PCR analysis revealed mRNA expression of AR both in congenital undescended and in retractile testicles. Conclusions The presence of AR in the epithelial cells of AT in patients with retractile testicle and its absence in patients with congenital undescended testis can be a possible cause of the effectiveness of hormonal treatment in retractile testis and its inefficacy in patients with congenital undescended testis.