This study contends that males with the fragile X syndrome feature problems in the visuospatial sphere as compared with Down syndrome males matched on vocabulary ability. Fragile X males suffer impairments of constructional functions, as demonstrated by their poor performance on block construction tests and on drawing tasks. These problems exist in association with visuoperceptive impairments, including the inability to reliably estimate angular relationships (Judgement of Line Orientation). They have shortened Digit and Corsi spans, and may feature some deficits in left hand co-ordination. The observation of a pervasive non-verbal deficit may also apply to carrier females, who despite functioning at an overall higher level, feature a similar pattern of deficits. It is possible that the deficit in non-dominant hemisphere functioning may be a pathognomonic feature of the chromosomal abnormality.