The impact of mitochondrial DNA haplogroups on the outcome of liver fibrosis was evaluated in 362 hepatitis C virus infection (HCV)-monoinfected and HIV/HCV-coinfected patients (147 and 215, respectively) in clinical follow-up at 2 reference hospitals in the Northwest of Spain. The mitochondrial DNA haplogroup H was the most prevalent (50.3%) in this population. The cluster Others and V were recognized as risk factors for the development of liver fibrosis while haplogroup H and HCV genotype 4 confer a lower risk. This information might be useful for prioritization of HCV treatment, especially for F0-F1 patients for whom there is no urgency for treatment.