All can be prevented by orchiopexy in cryptorchidism Except -
"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.
Testicular tumor
Epididymo orchitis
Torsion of testis
Sexual ambiguity