The appearance of blood in the seminal fluid is an alarming sign, with a rather inconstant origin. The causes of hematospermia are discussed based on a review of the literature and the authors' own experience with 84 patients. The importance of differential diagnosis is emphasized and a diagnostic scheme is presented. Therapeutic opportunities depending on etiology are discussed. It is concluded that although hematospermia is an often self-limiting sign, resolving in a few weeks, all patients should undergo a careful investigation to rule out the presence of malignancy or other significant disease.