Assessing for an adequate immunological response to a pre-exposure course of hepatitis B vaccine is not routinely recommended in all vaccinated individuals. Current UK guidelines advise checking hepatitis B surface antibody titres only in those considered at high occupational risk such as healthcare and laboratory workers. We present a case of an infantry soldier who developed acute hepatitis B despite having a complete course of hepatitis B vaccinations. This case emphasises that hepatitis B is still an important differential diagnosis for all returning military personnel who present with compatible symptoms despite being vaccinated.