Background: increasing incidence of hepatitis C virus (HCV) infection in HIV-positive men having sex with men (MSM) has been described in recent years. We performed phylogenetic analyses of acute HCV infections to characterize the dynamics during the epidemic in Paris and evaluated associated sexually transmitted infections (STI). Methods: Sanger Sequencing of polymerase gene was performed. Maximum likelihood phylogenies were reconstructed using FastTree 2.1 under a GTR+CAT model. Transmission chains were defined as clades with a branch probability≥0.80 and intra-clade genetic distances <0.02 nucleotide substitutions per sites. STI detected ≤1 month before HCV diagnosis were considered. Results: among the 85 studied patients, at least 81.2% were MSM. Respectively, 47.6%, 39.0%, 11.0% and 2.4% were infected with genotype 1a, 4d, 3a and 2k. At least 91.8% were HIV co-infected. HCV reinfection was evidenced for 24.7% of the patients and STIs for 20.0% of them. Twenty-two transmission chains were identified, including 52 acute Hepatitis C (11 pairs and 11 clusters from 3 to 7 patients). Conclusions: these results revealed a strong clustering of acute HCV infections. Thus, rapid treatment of not only chronic but also acute infections is needed among this population to decrease HCV prevalence, in combination with preventive behavioral interventions.