Group B streptococci colonize the nasopharynx, digestive tract and vagina. Most isolators are identified as S. agalactiae. Despite the fact that the microorganism can be isolated from the vagina with 25-45% pregnant women, the main reservoir is considered to be the digestive tract. In terms of serology, group B streptococci can be divided into serovars Ia, Ib, Ic, II and III. Serovar bacteria are trophic to the tissue of the central nervous system and respiratory tract and most often cause meningitis with neonates. The way of contamination is the advancing of the fetus through the generative passage infected by streptococci. Streptococcal pneumonia develops with respiratory viral infections in the background, ‘pure’ bacterial lesions occur very rarely but as a complication of the acute respiratory viral disease, pneumonia is quite common. Extensive contamination with respiratory viruses makes the pulmonary tissue more sensitive to bacterial superinfections as soon as a few hours after the permeation of the primary infection agent. The lesions caused by group B streptococci are found in all age groups but neonate pathology is absolutely predominant. With 30% children who display early manifestations, bacteriemia can be observed (with no specific primary contamination nidus), with 32-35% pneumonia can be detected, others are affected by meningitis with 50% developing it within 24 hours. The diseases with neonates take a grave course and the death rate reaches 37%. With children who display tardy manifestations meningitis and bacteriemia can be observed, 10-12% children usually die and 50% survivors have residual lesions. With women in labour group, B streptococci cause postpartum infections – endometritis, urinary tract disorders, operative wound complications after cesarean section. The microorganisms have been noticed to be apt to cause cutaneous integument and fleshy tissue lesions, pneumonia, endocarditis and meningitis with adults. Bacteriemia can also be observed with elderly people who suffer from diabetes mellitus, peripheral vessel disorders, liver diseases and malignant new growths.