Summary Mycosphaerella leaf diseases represent one of the most important impediments to Eucalyptus plantation forestry. Yet they have been afforded little attention in Uruguay where these trees are an important resource for a growing pulp industry. The objective of this study was to identify species of Mycosphaerellaceae and Teratosphaeriaceae resulting from surveys in all major Eucalyptus growing areas of the country. Species identification was based on morphological characteristics and DNA sequence comparisons for the Internal Transcribed Spacer (ITS) region of the rDNA operon. A total of ten Mycosphaerellaceae and Teratosphaeriaceae were found associated with leaf spots and stem cankers on Eucalyptus. Of these, Mycosphaerella aurantia, M. heimii, M. lateralis, M. scytalidii, Pseudocercospora norchiensis, Teratosphaeria ohnowa and T. pluritubularis are newly recorded in Uruguay. This is also the first report of M. aurantia occurring outside of Australia, and the first record of P. norchiensis and T. pluritubularis in South America. New hosts were identified for Kirramyces gauchensis, M. aurantia, M. marksii, M. lateralis, M. scytalidii, P. norchiensis, T. molleriana, T. ohnowa and T. pluritubularis. Interestingly K. gauchensis, which has been known only as a stem pathogen, was isolated from leaf spots on E. maidenii and E. tereticornis. The large number of Mycosphaerellaceae and Teratosphaeriaceae occurring in Uruguay is disturbing and raises concerns regarding the introduction of new pathogens that could threaten not only Eucalyptus plantations but also native forests.