This letter proposes a general closed-form formula of the Cramer-Rao lower bound (CRLB) for hybrid time-of-arrival/angle-of-arrival (TOA/AOA) target localization. The necessary and sufficient conditions on the existences of the CRLBs for hybrid TOA/AOA, TOA and AOA schemes are all presented. For a given localization scenario, the best achievable accuracy of the hybrid TOA/AOA scheme has been theoretically proved to be better than that of any one of the TOA and AOA schemes. With this hybrid scheme, the stringent time synchronization requirement of the localization system can be relaxed and the number of receivers can be reduced compared to the TOA scheme.