ALTHOUGH THE LITERATURE CONTAINS NUMEROUS REFERENCES TO FAMILIAL AGgregation of strabismus,1h3 multiple questions remain as to the precise mode of transmission. Are we dealing with a polygenic trait, as is commonly believed or a Mendelian trait, or even a nongenetic disease? The older analyses often dealt wih strabismus as the phenotype rather than with specific subtypes, such as accommodative esotropia, exotropia, or congenital esotropia. If such pooling were valid, analysis should give the same results in the subtypes as in the aggregate sample. In addition, conclusions were drawn from individual pedigrees, but to date none of the analyses have employed modern segregation analysis of large groups of families sampled in a systematic way with consistent clinical definitions. Thus, in spite of multiple extensive investigations into a possible genetic basis for eye disorders such as this, the question of etiology is unsolved to date, and hence this study was undertaken.