Testosterone is the main hormonal agent used for cross-sex hormone therapy in female-to-male transgender persons. Our aim was to systematically review the literature concerning the effects of testosterone on body mass index (BMI), blood pressure, hematocrit, hemoglobin, lipid profile, and liver enzymes in transgender men. PUBMED and EMBASE were searched for studies published until March 2017. Studies were included if they reported interventions with any dose of testosterone and comparison of variables before and during treatment. Of 455 potentially eligible articles, 13 were reviewed. Study duration ranged from 6 to 60 months, sample size ranged from 12 to 97 patients, and the most common treatment was parenteral testosterone undecanoate 1000 mg/12 weeks. Slight but significant increases in BMI were reported (from 1.3 to 11.4%). Three out of seven studies assessing the impact of different testosterone formulations on blood pressure detected modest increases or clinically irrelevant changes in this variable. In another study, however, two patients developed hypertension, which was resolved after cessation of testosterone therapy. Decreases in HDL-cholesterol and increases in LDL-cholesterol were consistently observed. Eight studies observed a relationship between testosterone and increased hemoglobin (range: 4.9-12.5%) and hematocrit (range: 4.4-17.6%), but discontinuation of androgen therapy was not necessary. In one study, two patients developed erythrocytosis (hematocrit >52%) after 9 and 12 months of treatment. One study analyzing testosterone formulations observed smaller increases in hemoglobin and hematocrit with testosterone gel. Six studies assessing liver function showed slight or no changes. Overall, the quality of evidence was low, given the lack of randomized clinical/controlled trials and the small sample sizes. In conclusion, exogenous testosterone administration to transgender men was associated with modest increases in BMI, hemoglobin/hematocrit, and LDL-cholesterol, and with decreases in HDL-cholesterol. Long-term studies are needed to assess the long-term risks of testosterone therapy, particularly as they relate to cardiometabolic risks such as diabetes, dyslipidemia and the metabolic syndrome.