C. trachomatis, the causative agent of hyperendemic trachoma and lymphogranuloma venereum, is also responsible of sexually transmitted infections. It is now recognized that genital chlamydial infections are the major cause of sexually transmitted diseases in Western industrialized countries, surpassing the importance of gonococcal infections. C. trachomatis, obligate intracellular parasite, enters the epithelial cells of genital mucosae and can reach, luminally, other organs of both female and male genital tract originating different clinical pictures. Vertical transmission of the microorganism from the infected mother to the newborn is of great importance. The infection takes place during delivery and can lead to disease in the newborn such as inclusion conjunctivitis and interstitial pneumonia. The present review deals mainly with clinical features and the most frequent complications of chlamydial infections. The identification of subjects at risk and the improvement of diagnostic techniques is of utmost importance since a prompt antibiotic treatment can eradicate the microorganism at least in uncomplicated infections, preventing the sequelae of the disease.