Abstract Introduction : Affordable and sensitive screening methods for acute hepatitis C (HCV) are necessary to successfully intervene in the current HCV epidemic among HIV‐positive men having sex with men. HCV core antigen (Ag) testing has been proven effective in diagnosing chronic HCV‐infected patients at low costs. We studied the characteristics of HCV Ag testing in acute HCV‐infected HIV‐positive patients. Methods : Plasma samples were selected from acutely HCV genotype 1‐infected patients treated with peginterferon, ribavirin and boceprevir in the Dutch Acute HCV in HIV Study. The control group consisted of HIV‐positive patients with a newly raised alanine aminotransferase (ALT) (>41 U/L) in whom HCV RNA was undetectable and who were tested for HCV Ag. Spearman correlation coefficient between HCV RNA and HCV Ag was calculated together with the sensitivity and specificity of HCV Ag testing at acute HCV diagnosis. Results and discussion : Upon acute HCV diagnosis, HCV Ag was identified in 39 out of 44 patients with detectable HCV RNA levels. In all 23 control patients without detectable HCV RNA in plasma, HCV Ag was undetectable as well. This resulted in a sensitivity and specificity of HCV Ag of respectively 89% (95% CI 75–96) and 100% (95% CI 82–100). The correlation between HCV Ag and HCV RNA was 0.97 ( p < 0.001) upon diagnosis. Conclusion : The data presented in this study suggest that HCV Ag testing is a sensitive and specific method that can be used in diagnosing AHCV in HIV‐infected patients.