HCV genetic diversity is high and impacts disease progression, treatment and drug resistance. HCV subtype 1a is divided in two clades (I and II), and the 80 K natural polymorphism in the viral NS3 protease is prevalent in clade I. Paradoxically, countries dominated by this clade have contrasting frequencies of 80 K. Over 2,000 HCV 1a NS3 sequences were retrieved from public databases representing Europe, Oceania and the Americas. Sequences were aligned with HCV reference sequences and subjected to phylogenetic analysis to investigate the relative presence of different subtype 1a clades and NS3 protease mutations. HCV-1a sequences split into clades I and II. Clade I was further structured into three subclades, IA to C. Sub-clade IA prevailed in the U.S., while subclade IC was major in Brazil. The NS3 80 K polymorphism was associated with subclade IA, but nearly absent in subclades IB and IC, a pattern similarly seen for the 91S/T compensatory mutation. Three HCV-1a-I sub-clades have been identified, with different frequencies in distinct regions. The 80 K and 91A/S mutations were associated with subclade IA, which provide an explanation for the disparities seen in simeprevir resistance profiles of countries dominated by HCV 1a-I, like the U.S. and Brazil.