Genotyping of the dentatorubral-pallidoluysian atrophy (DRPLA) locus in six patient samples, representing four normal individuals and two DRPLA patients, was successfully obtained using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). DRPLA is a dominantly inherited neurodegenerative disorder associated with the expansion of an unstable trinucleotide (CAG) repeat. The accurate determination of repeat length utilizing MALDI supports the use of this methodology for the analysis of genes containing unstable CAG trinucleotide repeats.