Several studies have reported in schizophrenia a decrease of age of onset in successive family generations, and this observation is consistent with anticipation. Anticipation is known to result from expansion of CAG repeats in several neurodegenerative disorders. Longer alleles of the KCNN3 gene, which contains a highly polymorphic CAG repeat, and encodes a neuronal small conductance calcium-activated potassium channel, have recently been shown to be over-represented in sporadic cases of schizophrenia. In this report, we tested the hypothesis of an association between longer alleles of CAG repeat in the KCNN3 gene and schizophrenia in 20 families with clinical evidence for anticipation and in 151 unrelated schizophrenic cases. No significant difference in the distributions of allele frequencies was observed between familial cases of schizophrenia and controls, and between unrelated cases and controls. Furthermore, no intergenerational CAG repeat instability was detected in the 20 families. Our results do not support the involvement of the KCNN3 (hSKCa3) gene in the etiology of schizophrenia.