The structure of CACNA1I, the gene encoding alpha1I, a human brain T Ca2+ channel alpha1 subunit, was determined by comparison of polymerase chain reaction-amplified brain cDNA and genomic sequences. The gene consists of at least 36 exons spanning at least 115,168 basepairs of chromosome 22q12.3-13.2. The predicted protein has 2016 amino acids and 28 potential phosphorylation sites. Alternative splicing of the gene occurs at two sites: cassette exon 9 and an alternative acceptor in exon 33. Molecular diversity generated by alternative splicing and post-translational modification of this and other members of the T alpha1 subunit gene family may account for the observed heterogeneity of T currents in central neurons.