Premature adrenarche was previously thought to be a benign condition. However, the authors and several other research groups have noted hyperinsulinism and insulin resistance in many girls with premature adrenarche. African-American and Caribbean-Hispanic girls with premature adrenarche are frequently obese with marked hyperandrogenism, signs which correlate with the degree of insulin resistance (i.e., those girls who are obese and insulin resistant tend to have higher levels of adrenocorticotropic hormone-stimulated androgens). Also, girls with premature adrenarche and reduced insulin sensitivity can have subtle decreases in their high-density lipoprotein (HDL) profile. Many of these girls have a strong family history of type 2 diabetes mellitus. Preliminary data regarding long-term follow-up of girls with premature adrenarche indicate that those girls who remain obese are at risk of developing polycystic ovary syndrome (PCOS). The term 'syndrome X' refers to the constellation of laboratory and clinical findings associated with hyperinsulinism stemming from insulin resistance. These findings include obesity, acanthosis nigricans, glucose intolerance, type 2 diabetes mellitus, dyslipidaemia with reduced HDL and elevated low-density lipoprotein, cardiovascular disease and PCOS. Hence, for certain girls, premature adrenarche may be a part of the clinical spectrum of syndrome X.