Circoviral infections in swine have appeared only recently and they today attract the attention of large numbers of researchers all over the world. They represent a great mystery, an unknown in veterinary medicine, both in our country and in the world. The causes of these infections are circoviruses, called after the DNA which is shaped like a circle. A large number of authors today believe the PCV-2 causes two pathological entities in weaned piglets which are known as porcine multisystemic wasting syndrome (PMWS) and porcine dermatitis nephropathy syndrome (PDNS). Current investigations indicate that there is a causal connection between these two syndromes. These two new diseases, which have recently spread all over the world, cause serious losses, great concern and confusion, especially when they occur simultaneously or in a sequence in the same herd, or in parallel with other pathogenes, primarily with the porcine reproductive and respiratory syndrome virus (PRRSV) and the porcine parvovirus (PPV). PMWS was first described in Canada in 1991. It most often affect pigs aged 5-12 weeks. The main clinical expression, depending on the stage of progression is diarrhea, delayed development or depressed growth, stuntedness, dyspnea ictherus, eyelid swelling, and lymphadenopathy. More rarely, there are neurological symptoms. Prominent suppression of the immune system is the main characteristic of PMWS, and a wave of secondary bacterial infection is also observed. PDNS is a new disease of economic importance, which mostly affects older swine, from 5 weeks to 5 months of age. The most prominent clinical symptoms in seriously ill piglets is extensive dermatitis, mostly on the chest, abdomen, haunches and forelegs, with the appearance of purple-red swellings of different shape and size. The swine are depressive febrile, anorectic, all of which leads to stunted growth. They are inactive. Mortality is often about 15%. PDNS is a differentially diagnostically significant disease because it can easily be mistaken for classic or African swine plague. These two syndromes still have not been recorded in our country. However, if one takes into consideration the fact that the virus is very resistant in the outer environment, that transmission is most frequently through infected swine, we can soon expect them to be detected in our country as well. This will be the case especially if investigations focus on improving and updating their diagnostics.