Gambierdiscus is a genus of benthic dinoflagellates that produce ciguatoxins (CTXs) and maitotoxins (MTXs), which are among the most potent marine toxins known. CTXs are bio-accumulated and biotransformed along the marine food chain and are involved in Ciguatera Fish Poisoning (CFP). Several species have recently been described, and CFP has recently been reported from non-endemic areas, namely the Canary Islands. Little is known about how toxicity varies among species and isolates of Gambierdiscus. This study examined the toxicity of 13 strains of Gambierdiscus, seven from the Pacific Ocean (G. pacificus CCMP 1650, G. sp. VGO 917, G. australes CCMP 1653, G. scabrosus KW070922_1, G. sp. Vietnam, G. caribaeus BILL HI Gam8, G. carpenteri PAT HI Jar7 Gam11), one from the Mediterranean Sea (G. carolinianus Greece Gam2), and five from the North-Eastern Atlantic Ocean (G. australes VGO 1178, G. australes VGO 1181, G. silvae VGO 1167, G. silvae VGO 1180, G. excentricus VGO 791). Algal cells were extracted with methanol, and extracts were partitioned between dichloromethane and aqueous methanol. The toxicity of pre-purified extracts has been evaluated using an ouabain/veratridine neuro-2a assay and a human erythrocyte lysis assay. In general terms, all strains showed hemolytic activity in the aqueous methanol fraction in the range of pg MTX eq/cell, and neuro-2a cytotoxicity in the dichloromethane fraction in the range of fg P-CTX-3C eq/cell. G. excentricus (Canary Islands) was an exception, with a neuro-2a cytotoxicity in the range of pg P-CTX-3C eq/cell, in accordance with data previously reported by Fraga et al. (2011).