Untreated sexually transmitted infections (STIs) can indeed lead to Pelvic Inflammatory Disease (PID) in women. PID occurs when bacteria from an untreated STI, such as chlamydia or gonorrhea, spread from the vagina or cervix to the uterus, fallopian tubes, or ovaries. This can cause inflammation and infection in these reproductive organs, leading to symptoms such as pelvic pain, abnormal vaginal discharge, and fever. If left untreated, PID can result in long-term complications like infertility, chronic pelvic pain, and ectopic pregnancy. Therefore, it is crucial to seek prompt treatment for STIs to prevent the development of PID.