SUMMARY.- Cercospora Leaf Spot (CLS) of olive is an important fungal disease in Uruguay, causing severe early defoliation. Fungal isolates were obtained from olive leaves with typical CLS symptoms from Uruguayan orchards. The isolates were identified based on phenotypic characteristics and DNA sequence analyses. Infection processes under field conditions were characterized. Phylogenetic analyses confirmed that Pseu-docercospora cladosporioides is the causal agent of CLS in Uruguay. Three colony morphologies were observed for isolates growing on potato dextrose agar. Mean conidium length ranged from 65.7 to 101.8 µm, and widths from 4.3 to 5.0 µm. Mean optimum growth temperature was 21.5°C (range 19.2 to 24.8°C). Under field conditions, initial CLS symptoms on leaves were observed 5 months after inoculation of cv. Arbequina plants, confirming the disease?s lengthy incubation period. This study shows that CLS as one of the most prevalent and destructive olive diseases in Uruguay, and emphasizes the importance of further research to develop efficient management of this disease. © 2023 P. Lombardo, C. Leoni, S. Alaniz, P. Mondino. This is an open access, peer-reviewed article published by Firenze University Press (http://www.fupress.com/pm) and distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. All Rights Reserved.