AbstractWe report on 4 new cases of mildly retarded patients with marfanoid habitus and a characteristic constellation of minor anomalies. These patients, although sporadic, are likely to be affected by the same X‐linked type of mental retardation described by Lujan et al. (American Journal of Medical Genetics17:311–322,1984) and more recently by Fryns and Buttiens (American Journal of Medical Genetics28:267–274, 1987).The similar psychiatric history in 2 of our patients suggests that psychotic behaviour could be an additional manifestation, previously unrecognized in this condition.Late diagnosis of this relatively new syndrome in all our patients confirms the difficulty of the nosologic definition of mentally retarded individuals on clinical grounds alone. On the other hand, the Lujan‐Fryns syndrome appears to be more common than one would have