**1. Introduction**

Cryptorchidism or undescended testis (UDT) is the most common genital abnormality seen at term in boys (Meij-de Vries A et al 2010, Topari & Kalieva 1999 ). Traditionally UDT was thought to be a congenital disease, with a prevalence of about 0.8-1% by 1 year of age (Berkowitz G Set al 1993). The term acquired UDT was introduced the last few decades, after well documented clinical observations in individuals and groups of patients that many boys continue to be diagnosed and treated later in childhood (Myers NA & Officer CB 1975, Atwell JD 1985, Clarnette TD et al 1977, Schiffer KA et al 1987, Robertson JF & Azmy AF 1988, Wright JE 1989, Fenton EJM et al 1990,Mayr J et al 1995) despite the recommendations for early surgical treatment by orchidopexy (Ritzén M et al 2007). Today, acquired UDT is a recognized separate entity, and after a new clinical classification in 2003, UDT is categorized into two forms: congenital UDT and acquired UDT (Hack WW et al 2003a).

Although the pathogenesis of congenital UDT is considered multifactorial including hormonal, genetic, and environmental influences (Ghacko JK & Barthold JS 2009, Barthold JS 2008 ), the exact etiology of acquired UDT remains unclear (Meijer RW 2004). Furthermore, while surgical treatment is recommended for congenital UDT patients as young as 6 months (Ritzén M, 2007), to reduce the increased risks of progressive infertility, testicular malignancy, torsion, associated inguinal hernia, and because of cosmetic and psychological aspects (Ashley RA et al 2010, Lamah M et al 2001) there is much controversy in the management of acquired UDT (Hack WW et al 2010).

In this article, we present the current data of the literature of this distinct entity in a concise but comprehensive review.
