Recently many South American Vismia species and African Psorospermum species belonging to the Vismieae tribe of Hypericoideae have been examined, resulting in the isolation of 12 vismiones (limited to this tribe) characterized by a tetrahydroanthracene nucleus with a non-aromatic A ring, differing in substituents at C-6 (OH/OAc), C-3 (OH/OMe/OPr/O-geranyl), and C-2 (mono-/di-prenyl; side chain at C-10 only in vismione G). Chemotaxonomically, vismiones with a five-carbon side chain at C-2 are mainly from Vismia, while those with a geranyl chain are from Psorospermum. Vismiones and other Vismieae secondary metabolites showed good antifeedant activity against Lepidoptera larvae and Locusta migratoria but no antibacterial or antifungal activity. This paper deals with the cytotoxicity of vismiones and preliminary in vivo antitumor activity data of vismione A (NSC 339659). Among prenylated anthranoids from Vismieae, only vismiones displayed significant cytotoxicity against different tumor cell lines. The efficacy of vismiones in inhibiting the growth of 9 KB, doxorubicin-sensitive (P-388/S), and doxorubicin-resistant (P-388/R) P-388 leukemia cell lines was tested. Data showed that vismione D and F with a C-6 acetoxy group were more effective than their C-6 hydroxylated counterparts, and compounds 3 and 4 were slightly more effective against P-388/R than P-388/S. Vismione A, the most effective against 9 KB in vitro, showed significant in vivo activity against M 5076 ovarian carcinoma and B 16 melanocarcinoma in mice but was inactive against P-388 ascitic leukemia.