12 A hybrid pulse interval modulation--code-division multiple- access (PIM-CDMA) is proposed for optical wireless communication systems. It offers higher transmission rate compared with the hybrid pulse position modulation (PPM)-- CDMA due to its non-fixed frame structure. Strict optical orthogonal code is used as a signature sequence located at the start each frame. Expressions for bit error rate are given for both PPM-CDMA and PIM-CDMA schemes, assuming that the dominant noise and interference are due to the self- interference and optical multiple access interference. The numerical results are compared with both PPM-CDMA and OOK- CDMA, and it shows that the proposed scheme is a viable scheme for optical wireless communications.