Myotonic dystrophy 1 is caused by the expansion of a CTG trinucleotide repeat on chromosome 19q13.3. The repeat lies in the 3' untranslated region of the myotonic dystrophy protein kinase gene (DMPK), and it has been hypothesised that the expansion alters the expression levels of DMPK and/or its neighbouring genes, DMWD and SIX5. Published data remain controversial, partly due to the mixed cell populations found in most tissues examined. We have microdissected human skeletal muscle biopsies from myotonic dystrophy 1 patients and controls and analysed gene expression at this locus for type I and type IIA fibres, using quantitative real-time reverse transcription-polymerase chain reaction. Levels of DMPK expression were specifically decreased in the type IIA fibres of myotonic dystrophy patients, below the levels found in controls. This suggests that DMPK expression is altered in this disease, suggesting significant pathological consequences.