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In spite of the great environmental and sanitary importance of cyanobacteria, their biodiversity is little known in Tunisia. In this work, a review was carried out, based on literature data, of potentially toxic cyanobacteria occurrence in Tunisia. Microcystis, one of the most widely distributed toxic bloom-forming cyanobacteria genera, was represented by Microcytis wesenbergii, found only in Lebna water reservoir, and Microcytis aeruginosa recorded in different water bodies. The invasive potentially toxic cyanobacterium Cylindrospermopsis raciborskii, reported for the first time in Tunisia in October 2004, was observed in the semi-arid to arid areas. The harmful genus Planktothrix was represented in Tunisian freshwater by the green-pigmented species P. agardhii. The filamentous cyanobacteria dominance is increasingly reported in Tunisia in eutrophic water bodies. This dominance increases especially during the summer-autumn period. Recently, potentially toxic cyanobacteria blooms have been reported in some reservoirs in the north east of the country. These blooms were generated by the potentially toxic Chroococcale Microcystis aeruginosa. Harmful cyanobacteria tend to spatio-temporal expansion in the Tunisian inland waters. The toxicological potential evaluated by several methods showed that none of the Tunisian strains were proved to be cylindrospermopsin nor saxitoxin producers. However, the majority of Microcystis were able to synthesize microcystin.