At present, PID is considered to be the most severe gynecological infection of young women as well as one of the most important problems of public health involving high social and economical costs. There are two pathogenetic aspects of PID. The primary form results from an ascending infection sustained by the microbic flora of the inferior genital tract, subsequently involving its higher anatomical districts. The secondary form derives from the pelvic diffusion of microorganism primarily involved in extra-genital infections. The analysis of the epidemiological aspects of the disease identifies in the sexual habits, the contraceptive procedures as well as the invasive instrumental practices (iatrogenic factors) the risk factors of the disease. PID has a multimicrobial origin based on a complex interplay between synergic infectious agents, vectors of etiological factors, interferon-gamma and intrauterine devices. The anatomopathological aspects of PID, including Fitz-Hugh-Curtis syndrome are discussed. The literature concerning the diagnosis and the therapy of the disease is extensively analyzed.