Two courses of LHRH nasal spray (400 micrograms three times a day for 28 days), partly administered in a double-blind placebo-controlled study, resulted in the descent of 48 of 281 testes (18%) in 237 prepuberal boys. Logistic regression analysis confirmed the clinical observation that pretreatment testicular position was the major factor influencing treatment results: the lower the pretreatment testicular position, the better the result. Of the unsuccessfully treated boys, 170 with 196 undescended testes subsequently underwent orchiopexy revealing anatomic anomalies that accounted for failure of hormonal treatment in 80% of the cases. Most frequent finding amounted to an underdeveloped processus vaginalis, extending no further than the level of the pubic bone, often associated with major epididymal deformities and a lack of obliteration of the processus vaginalis (107 of 196 operations). Obstruction of the scrotal entrance due to abnormal Scarpa's fascia or abnormal gubernacular remnant was found in 35 and testicular absence in 15 cases. LHRH nasal spray might be effective when the testis can be manipulated to at least the scrotal entrance before treatment, but in view of our surgical findings, LHRH nasal spray will not replace orchiopexy.