Pyridoxine Dependent Seizures (PDS) is a rare, autosomal recessively inherited disorder. Recently alpha- aminoadipic semialdehyde (α-AASA) dehydrogenase deficiency was identified as a major cause of PDS, which causes accumulation of both α-AASA and pipecolic acid (PA) in body fluids. We studied urinary and plasma & [alpha]-AASA and PA levels in 12 Dutch clinically diagnosed PDS patients. In 10 patients, α-AASA was elevated in both urine and plasma. In these patients plasma PA levels were also elevated but urinary PA levels were normal. In all patients with clinically definite PDS, and in most patients with probable or possible PDS, the clinical diagnosis of PDS could be confirmed at the metabolite level. Non-invasive, urinary screening for α-AASA accumulation provides a reliable tool to diagnose PDS and can save a patient from the classical and potentially dangerous "pyridoxine withdrawal test" to prove PDS.