Self-compacting concrete (SCC) can be placed and compacted under its own weight. Modifications in the mix design of SCC may significantly influence the material's mechanical properties. Therefore, it is vital to investigate whether all the assumed hypotheses about conventional concrete also hold true for SCC structures. This paper discusses an experimental programme that was carried out to study the effects of specimen size and shape on the compressive and tensile strength of SCC and fibre reinforced SCC. For this purpose, cube specimens with 100 and 150 mm dimensions and cylinder specimens with 100 3 200 and 150 3 300 mm dimensions were casted. The experimental programme examined four SCC mixtures: plain SCC, and steel-, polypropylene- and hybrid-fibre reinforced SCC. Compressive and tensile strengths were tested after 3, 7, 14, 28 and 56 days. The paper also investigates correlations between compressive and tensile strengths and the size and shape of the specimen.