Background: Vaccination against hepatitis B is now recommended as a universal vaccination for infants, children and adolescents. Pre-vaccination serological screening and testing of the response to the vaccine is not performed routinely in this context. Casuistic: After 5 vaccinations with a genetically engineered vaccine against hepatitis B, a 22-year-old medical student did not develop protective immunity. Serological tests revealed chronic infection with the hepatitis B virus. The so called “non-responder” had already been infected with hepatitis B. Conclusion: In occupational medicine, pre-vaccination, serological screening and the checking of the response to the vaccine should be obligatory. Persons who do not respond to the vaccine may already have been infected with the hepatitis B virus. In these cases additional serological tests must be performed to rule out chronic infection. If chronic infection is not identified, adequate therapy cannot be carried out in time. This might lead to serious complications and the spreading of the disease in the private and the occupational field.