The cytosolic aryl sulfotransferase genes SULT1A3 and SULT1A4 are located on chromosome 16p11.2 in a region of chromosomal instability. SULT1A3/4 are important enzymes in the metabolism of catecholamines linked to neurodegenerative diseases such as Parkinson’s and Alzheimer’s. In the present study, copy number variation of the SULT1A3/4 genes in healthy individuals, as well as a cohort of Parkinson’s disease and Alzheimer’s disease patients was examined. In all subjects, SULT1A3/4 copy number varied from 1 to 10. In Alzheimer’s disease patients, there was a significantly lower copy number compared to controls, and a positive correlation between copy number and age of disease onset. By contrast, there were no differences in Parkinson’s disease patients. However, when early-onset Parkinson’s disease was evaluated separately, there appeared to be an association with gene copy number and risk. The current study shows that these neurodegenerative diseases may be related to SULT1A3/4 copy number.