Cyanobacteria are aquatic micro-organisms that pose a great threat to aquatic ecosystems by the production of dense blooms, but most importantly by the production of secondary metabolites, namely the cyanotoxins. One of these is cylindrospermopsin (CYN), a hepatotoxic polyketide-derived alkaloid with well-known associated cases of animal mortalities and human morbidity. First described as being associated with liver damage, this toxin is now considered a cytotoxic and a genotoxic toxin, due to its effects in other organs and in DNA. Its occurrence has been reported so far in eight different cyanobacteria species and in several water samples from four of the five continents. With a guideline value of 1 μg l−1, CYN is now considered the second most studied cyanotoxin worldwide. It is important to review the information regarding the findings made until now about this cyanotoxin 30 years since its first report.