Background: Strong evidence from twin and family studies suggests that the genetic liability to autism may be expressed through personality and language characteristics qualitatively similar, but more subtly expressed than those defining the full syndrome. This study examined behavioral features of this "broad autism phenotype" (BAP) in relation to performance on a measure of social-cognition in an attempt to tease out this complex clinical picture and identify markers of underlying neuropsychological systems of genetic significance to autism. We hypothesized that mild social-cognitive impairment would be associated with clinically defined social characteristics of the BAP (aloof personality style, lower quality social relationships, and impaired pragmatic language use). Method: Forty-eight parents of individuals with autism (13 of whom were identified as "aloof"), and 22 control parents, were administered the "Eyes Test", a social-cognitive measure that taps the ability to read complex psychological states from viewing only the eye region of faces. Results: Whereas social-cognitive ability was unimpaired among parents of autistic children in general, the subgroup of parents defined as "aloof" displayed significant social-cognitive deficits on the "Eyes Test". Impaired social-cognitive ability was associated with low quality of friendships and problems with pragmatic language use, associations which mirror those documented in autism. Conclusions: Findings suggest that social-cognitive impairments co-segregate with conceptually related personality, social, and language features that constitute the BAP, and point towards performance on the Eyes Test as a genetically meaningful endophenotype.