The Peyronie's disease or Induratio Penis Plastica, represents one of the most controversial and uncertain points of the modern andrology, since its real etiology is still disputable. Consequently also the non-surgical therapy results as still confused and variable as shown in the considerable number of drugs utilized till now. Our study takes into consideration the injection therapy, by the use of the Betamethasone (corticosteroid), and it tries to explain, how it is possible, the real efficacy of drug versus placebo. The randomized study includes 30 patients. The valuation of the results has been effected in reference to three parameters: disappearance of pain, decrease of plaque volume and consistency of 50%, decrease subjective penile curvature. The data obtained show no significant differences between group A (treated with Betamethasone) and group B (treated with placebo). At twelve months of mean follow-up the pain at erection disappeared in 66.6% of the patients of group A, in 53.3% of the patients of group B. The curvature diminished in 20% of the patients of group A and in 26.6% of the patients of group B. A decrease in plaque volume and consistency was noted in 40% of the patients of group A and in 40% of the patients of group B. The data show that probably the clinical results of the therapy is to refer to a mechanical effect of injected volume and not to the drug action itself.