The optical rotations (ORs) of chiral organic molecules have been calculated by time-dependent density functional response theory (TDDFT) employing the B3LYP hybrid functional. For selected examples, the origin as well as the frequency dependence of the OR has been investigated. The theoretical data for 20 organic molecules including large systems as e.g., octahelicene compare favourably with experimental observations even if small valence basis augmentented with diffuse basis functions are employed. The inclusion of the frequency dependence in the theoretical treatment is recommended to obtain reliable predictions for measured OR values.