Introduction: Erectile dysfunction (ED), also known as impotence, is defined as a consistent or recurrent inability to attain and/or maintain penile erection sufficient for sexual performance [1]. According to recent study results, ED occurs more than 50% over 60 year old males, emphasizing a need to diagnose and treat it at an earlier stage. ED may be assessed in several ways. The most widely used standardized questionnaire is the International Index of Erectile Function (IIEF) with 15 questions, which also exists in a short form with 5 questions [2]. On the other hand, ED is associated with a decreased level of androgens in aging males; the latter is often referred to as a Late Onset Hypogonadism (LOH) or Testosterone Deficiency Syndrome (TDS). In simple terms, LOH or TDS can be defined as a decreased serum testosterone level in aging males [3, 4]Objective: To detect the testosterone deficiency syndrome in aging males with erectile dysfunction. Materials and Methods. 309 males over 40 years of age who received medical care at the ADAM urological and andrological clinic from 2010 to 2011 were included in this study. An approval of the Ethical Committee of MOH was obtained at the commencement of the study. Each study participant signed a consent form at the beginning of the study. Each participant was assigned to either an ED group or a control group depending on results of the IIEF-5 questionnaire. The ED group was further divided into three groups (moderate, severe and very severe) based on a level of ED. The total testosterone (TT) levels were determined in blood serum, using a competitive ELISA analytical system UBI MAGIWELTM TestosteroneQuantitative test (GLS, USA), with C.V. (%) 6.8 and free testosterone (FT) calculated as described by Vermeulen. Test samples were collected between 8.00-11.00 am. The biochemical diagnosis of TDS was based on the Study Aging Male (ISSAM) guidelines of the International Society, particularly, if TT was _3.46 ng/ml or free testosterone FT was ≤0.072 ng/ml [5].Results: ED of moderate, severe and very severe levels were diagnosed in 199 (64.41%) out of 309 participants. There was an inverse association between an erectile function and age (r=-0.380, p <0.01). The average TT was 5.75±2.316 ng/ml and FT was 0.091±0.0084 ng/ml. Compared to the ED group, the control group had a higher TT level: 5.6440±1.177 ng/ml and 5.812±2.316 ng/ml respectively. In the control group the FT level was 0.061±0.0084 ng/ml whereas it was 0.041±0.0076 ng/ml in the ED group. Conclusion: Our study showed that most of aging males who came to the clinic had a moderate to very severe ED (64.55%). The level of TT (5.644±1.177 ng/ml) and FT (0.041±0.0036 ng/ml) was significantly lower in ED patients (p<0.05). The testosterone deficiency syndrome was detected in 24.27% of the ED group.