By this case report the authors will emphasize the importance of systematic psychiatric exploration in clinical practice with gender identity disorders. Standard procedures have diagnostic and differential diagnostic purpose (exclusion of other psychiatric disorders or comorbid psychiatric disorders).

Presented patient is 20 year old female who addressed to Belgrade Team for Gender Identity for routine psychiatric exploration with suspicion of female-to-male transsexualism. As a contribution to mentioned diagnostic category the authors have noted long term persistence of gender dysphoria through puberty and adolescence, persistent wish for partial sex reassignment surgery, specific defense mechanisms and intake of testosterone without medical prescription.

Applied diagnostic procedures and complementary analysis (EEG, NMR) have imposed doubts in primarily suspected transsexualism and leads us toward differential diagnosis analysis for organic or psychotic mental disorder.