Classical swine fever (CSF) is a highly contagious disease causing major losses in pig populations almost worldwide. The disease occurs in many regions of Asia, Central and South America and parts of Europe and Africa. Some countries have eradicated the disease (Australia, USA, Canada, within the EU), yet it keeps recurring sporadically (South Africa, Germany, Netherlands, England). The causative virus is a member of the genus Pestivirus, family Flaviviridae. The first diagnosis of CSF is based on the recognition of clinical signs by the veterinarian in the field and by post mortem findings. Many signs are not exclusively associated with CSF and they may vary with the strain of virus, age and health status of the pigs. Since clinical signs may be confused with other pig diseases, laboratory diagnosis of CSF is indispensable. Both the Office International des Epizooties (OIE) and the European Union, have approved diagnostic manuals establishing sampling methods and diagnostic procedures for the confirmation of the disease. In this review, experiences with current tests will be analyzed and complemented with new developments, with emphasis on the polymerase chain reaction after reverse transcription of the RNA genome (RT-PCR).