A patient with beta hCG-secreting germ cell carcinoma of the pineal and suprasellar regions presented with hydrocephalus, Parinaud's syndrome, hypopituitarism and polyuria. Central diabetes insipidus was strongly suspected although the water deprivation test was not diagnostic. The polyuria however, responded to ADH analogue when the hypothyroidism and hypocortisolism were treated. Pubertal development was evident and serum testosterone was normal despite the low FSH/LH, suggesting hCG stimulation of Leydig cells. This case illustrates that a beta hCG-germ cell tumour of the suprasellar region causing hypopituitarism can mask the presence of central diabetes insipidus and hypogonadotrophic hypogonadism.