Summary.Previous investigations undertaken in Wales have yielded somewhat contradictory results concerning the influence of bilingualism on performance in non‐verbal tests of intelligence. More recent surveys, planned on a wider scale, consistently reveal a tendency for mean scores on such non‐verbal tests to decrease with increasing Welsh linguistic background, and also show statistically significant differences in favour of monoglot (English) groups by comparison with bilingual (Welsh) groups. In the present study, reference is made to a re‐analysis of the results of one of these large‐scale surveys in relation to the parental occupations of the pupils tested. The findings of this re‐analysis indicate that, whereas monoglot and bilingual groups which vary significantly in occupational class also differ significantly in non‐verbal intelligence, corresponding linguistic groups of comparable socio‐economic status do not differ significantly in this respect. It is, therefore, concluded that bilingualism need not be a source of intellectual disadvantage. The importance of a thorough examination of socio‐economic factors in any comparative study of monoglot and bilingual children is strongly emphasised, and a study of bilingualism and non‐verbal intelligence which appeared in a recent issue of thisJournalis critically examined on account of its defects in this and in certa