Blood serum levels of estradiol, progesterone and magnesium at the lutheal phase of the menstrual cycle in 13-18 years old girls with primary dysmenorrhea were investigated. Non-steroid anti-inflammatory drug was used for differential diagnosis. Rapid pain relief after nimesulid administration is typical for functional dysmenorrhea. The absence of drug effect, magnesium deficiency, relative hyperestrogenemia and hypoprogesteronemia are typical for primary dysmenorrhea.