Background: The term premature pubarche (PP) refers to the appearance of pubic hair before age 8 in girls and before age 9 in boys. Although idiopathic PP (often associated with premature adrenarche) is considered an extreme variation from the norm, it may be an initial sign of persistent hyperandrogenism. Factors contributing to PP onset and progression have not been identified to date. Aims: The objectives of this study are to describe a group of Italian children with PP, to identify potential factors for its onset, and to define its clinical and biochemical progression. Methods: We retrospectively enrolled all infants born between 2001 and 2014 with PP. Children with advanced bone age (BA) underwent functional tests to determine the cause of PP. Hormonal analysis and BA determination were performed annually during a 4-year follow-up period. Results: A total of 334 children with PP were identified: idiopathic PP (92.5%, associated with premature adrenarche in some cases); related to precocious puberty (6.6%); late-onset 21-hydroxylase deficiency (0.9%). Low birth weight was associated with premature adrenal activation. Body mass index (BMI) was the only factor that influenced the progression of BA during follow-up. Conclusions: Low birth weight is a predisposing factor for premature adrenal activation. The increase in BMI in patients with idiopathic PP during the 4-years of follow-up was responsible for BA acceleration. We recommend prevention of excessive weight gain in children with PP and strict adherence to follow-up in order to prevent serious metabolic consequences.