In a follow-up study during 20 years (1975-1994) we observed, beside clinical aspects, the evolution of pleuropneumopathies in infants and small children (1-3 years of age), and the etiology of these infections. The casuistry includes 456 children-237 infants (51,97%) and 219 small children, between 1-3 years of age (48,02%), which were admitted in Clinical Children's Hospital from Oradea (Clinical Hospital for Children) with pleuropneumopathies. 4 intervals of time were analyzed comparatively, each of 5 years, starting with a number of 235 cases in the first one and reaching only 45 observations in the last one. The etiology was dominated by coagulase-negative and coagulase-positive Staph, aureus (34,20-60,40%), Strept. pneumoniae (14,10-40,00%). From the Gram negative bacteria, there were identified Kl. pneumoniae (2,20-9,80%), Pseudomonas sp. (2,20-5,19%), E. coli and Proteus sp. (1,70-2,20%). There were 2,90-9,85% of cases with a potential of pathogenicity, in various associations. In the last 10 years, the number of cases with unprecised etiology is growing (22,50-33,30%) probably because of the implication of anaerobe and coagulase-negative staphylococci, no tests of isolation and identification being made for them.