Chlamydia psittaci infection (chlamydosis, psittacosis-ornithosis is a naturally occurring systemic disease of birds. It is recognized by thy World Health Organization as particularly dangerous for humans zooantroponosis. In the work are presented etiological, epidemiological, clinical and morphological studies on recent outbreaks of chlamydiosis in waterfowl, hens and other avian species, as well as in persons occupationally involved in the poultry industry. Employed were the methods of complement fixation test, isolation and cultivation of chlamydiae in chicken embryos, light and electron microscopy, histology, epidemiological analysis. Investigated were a total of 3707 birds and 408 persons involved in poultry industry. Chlamydial CF-antibodies were detected in ducks (16.49–25.20 %) in 13 foci, in geese (12.00–40.75 %) in 6 foci, hens (13.42–41.17 %) in 3 foci, as well as in pigeons, pheasants, parrots and magpies. Eight Chlamydia psittaci strains were isolated. Serological data for chlamydial infection were obtained in diseased and contact persons. The direct electron microscopy of C. psittaci in pathological materials from birds is a valuable method. Presented is ultrastructural characteristic of the chlamydiae, as well as the histological findings in the tissues of birds with chlamydiosis. The observed clinical course among the birds varied from acute to inapparent forms. The human clinical cases were manifested with expressed adynamics, febrile reactions, respiratory signs, interstitial pneumonia. The reported results may contribute for better understanding of the problem and for more efficient diagnosis and control of this zooantroponosis.