Mycoplasma pneumoniae was first isolated over 100 years ago. There are intensive researches on this atypical pathogen causing various diseases at humans, lasting for over 50 years. Progress of serological diagnostic possibilities, increasing sensitivity and specificity, influences various results of epidemiological researches. It allows recognition of MP infections in course of diseases previously not connected with atypical bacteria and it allows also to prove influence MP infections on classical pulmonary diseases. MP infections affect both children and adults. Mycoplasmatic infections do not respond to classical antibacterial treatment, intracellular drugs like macrolides bring treatment effect. Contact with MP bacteria is quite common, mostly non-symptomatic. Diseases caused by MP classically give respiratory tract symptoms and are easy to recognize, but there always is a possibility of appearance of extrarespiratory signs of Mycoplasma pneumoniae infections. Mostly they are mild, but they can appear as skin symptoms, motor system symptoms, such as erythema nodosum, erythema multiforme, infectious arthritis and others like examples described in the article. Nervous system and hematopoietic system signs are less common. There where also diagnosed acute pancreatitis, hepatitis, pericarditis and peritonitis. The last one can be caused by MP in patients with immunological deficiency.