This paper presents a study of digital pulse interval modulation (DPIM) as a candidate modulation scheme for optical wireless communications. DPIM code characteristics are discussed and the theoretical error probability performance of DPIM is analyzed in terms of the packet error rate. Performance comparisons are made with the more established techniques of on-off keying and pulse position modulation (PPM). We show that, for a simple threshold detector based receiver, DPIM can out perform PPM in terms of bandwidth efficiency and power efficiency, by taking advantage of its inherent variable symbol duration. Practical results are given for an experimental system in the form of eye diagrams. The use of a coding scheme with a non-uniform symbol duration does have implications for system design, which are discussed in the paper.