SummaryA comparative study of the number and type of phonological errors made spontaneously and in imitation by mental age matched normal, severely subnormal and Down's Syndrome children was carried out. The results indicated that the normal and severely subnormal non Down's Syndrome children performed equally, while the Down's Syndrome children made more errors, and those errors were more inconsistent as compared to the other two groups. The Down's Syndrome children made fewer errors in imitation than they did in spontaneous production.These findings were interpreted as an indication that phonological development is linked to general mental development in severely subnormal non Down's Syndrome children. The exceptional performance of the Down's Syndrome group was hypothesized to be partly due to a general difficulty in generating predetermined sequences of movements.