Five patients who were initially evaluated for malignant neoplasm actually had infectious syphillis (one primary, two secondaries, two secondaries with persistence of primary). Two patients were considered for radical surgery and one for extensive radiation and/or chemotherapy. In four patients an elevated routine admission VDRL was the first indication of the correct diagnosis. Dark-field examination is the most important laboratory test in the diagnosis of primary syphillis; VDRL and FTA-ABS are most important in confirming secondary syphillis. Penicillin remains the drug of choice for therapy. At a time when the incidence of sexually transmitted diseases is increasing, it is extremely important to develop adequate educational programs for medical students and physicians.