An undescended testicle occurs in about 3 percent of full-term baby boys but in as many as 45 percent of boys born prematurely, explains Matthew Mason, MD, a pediatric urologist at Upstate. The reasons why one testicle (or occasionally both) does not find its way to the scrotum are unclear, he says, noting that pediatricians check for this problem in well-child visits. Mason also describes aspects of the condition and possible complications, such as reduced fertility and testicular cancer, as well as treatment options.