African swine fever (ASF) was diagnosed for the first time in the Netherlands on a farm near The Hague, illegally feeding swill from hospitals, hotels and restaurants. Laboratory diagnosis was based initially on the indirect immunofluorescence test (IFT) and the immunoperoxidase monolayer assay (IPMA) for antibodies in tissue extracts and later on confirmed by the direct-IFT on cryostat sections, animal inoculation and haemadsorption. Clinical signs and post-mortem lesions were consistent with the subacute form of ASF. Mortality amounted to 19% over a period of three weeks. Forty-three sera collected from animals in stables with active disease were all found positive by the IPMA.