Viral arthritis is found in acute viral hepatitis, rubella, mumps, smallpox, arbovirus infection, infectious mononucleosis, etc. Arthritis rarely develops with influenza, arthralgia and myalgia associated with general intoxication are more common. The pathogenesis of joint damage during viral infections can be associated with the deposition of immune complexes containing the antigen, and with the direct effect of the virus on the synovial membranes. The characteristic signs of viral arthritis are the short duration of joint damage and usually the complete reversibility of the process. In acute viral hepatitis, arthralgia often develops, less often – migrating arthritis. Both small and large joints are involved in the process. Arthralgia or arthritis can appear in the prodromal period, disappearing in the midst of jaundice. Arthritis can be combined with hives and headaches. Sometimes the joint syndrome persists for several months, simulating a picture of RA. Cases of development of classical RA in patients with viral hepatitis are also described. With rubella, arthritis is often observed, mainly in women, as well as in children and adults after vaccination with a live vaccine. Symptoms of arthritis can be detected at the same time as the rash appears, or appear a little later. The most characteristic lesion of the small joints of the hands. The duration of arthritis is on average up to 2-3 weeks. Residual effects are usually absent, although the role of rubella virus in the development of RA is not ruled out. With mumps, arthritis is rare (in 0.5% of patients), more often in people over 20 years of age. It manifests itself on the 8-21st day from the onset of the disease, in some patients simultaneously with the development of mumps or even before the onset of swelling of the parotid glands. Typically, joints are affected in patients with bilateral lesions of the parotid glands, often along with other complications (orchitis, pancreatitis). The appearance of arthritis is accompanied by a new wave of increase in telag temperature. Swelling of the joints develops, movements become painful. The most characteristic lesion of large joints, but small joints of the hands and feet may be involved in the process. The duration of arthritis is from two to several months. It ends with a full recovery. Paraneoplastic arthropathies . Nonspecific osteoarticular changes observed in malignant tumors of various localization, within the framework of the paraneoplastic syndrome, can long precede the appearance of other symptoms of the tumor (“joint masks” of the tumors), develop simultaneously with them or later. The clinical manifestations of the disease are diverse. The most common are Marie-Bamberger syndrome (hypertrophic osteopathy), amyloid, dysmetabolic (gouty) arthropathy, nonspecific mono-, polyarthritis, arthralgia, tendovaginitis, myalgia.