All can be prevented by orchiopexy in cryptorchidism Except -
Testicular tumor
Epididymo orchitis
Torsion of testis
Sexual ambiguity
"All types of malignant testicular tumors are more common in incompletely descended testes even if they have been brought down surgically. However it does improve the prospect of early diagnosis." - Bailey
Undescended testis 

In undescended testis - the testes is arrested in some part of its path to the scrotum.
In Ectopic testis - the testis is abnormally placed outside its path.
Retractile testis - in infancy 80% of in apparent testis are retractile testis and require no t/t.
Approx 70-77% of cryptorchid testes will spontaneously descend, usually by 3 months of age.
More common in preterm, small for gestational age, LBW & twin neonates.
More common on t. Side*
Secondary sexual characteristics are normal

Complications of incomplete descent

Torsion of testis
Epididymo-orchitis
An associated indirect inguinal hernia is frequent
Atrophy
Pain - A testis situated in the inguinal canal is often liable to trauma and give rise to pain in the groin
Sterility - If the condition is bilateral
Malignancy - risk is 40 times more than a normally placed testis.