His research is mainly devoted to viral hepatitis and population-based liver diseases. Het contributes to investigator-initiated and multicenter international clinical trials on therapeutics for liver diseases, and leads a program on early detection and epidemiology of liver disease within the ERGO center in Rotterdam. During the last few years this meant a special focus on metabolic associated liver disease.

In the clinic he leads the abdominal sonography program of the department of Gastroenterology & Hepatology. He trains others in abdominal ultrasound, for scientific associations like the Netherlands Association for the Study of the Liver (NASL) and European Association for the Study of the Liver (EASL).

Furthermore, he is director of the training program in Gastroenterology & Hepatology, and Editor-in-chief of Magma, the journal of the Dutch Society of Gastroenterologists and Hepatologists.