Phytanic acid occurs in the human diet as a metabolite of the fatty acid side chain of chlorophyll. Due to the presence of an epimeric beta-methyl group phytanic acid cannot be metabolised via the well-characterised beta-oxidation pathway. Instead it is metabolised in the peroxisomes in a ‘preliminary’ alpha-oxidation pathway to give pristanic acid that is subsequently degraded via beta-oxidation. Phytanoyl-CoA 2-hydroxylase (PAHX), a ferrous iron and 2-oxoglutarate (2OG) dependent oxygenase, catalyses a vital step in the alpha oxidation pathway comprising hydroxylation of both epimers of phyatnoyl CoA. Mutations to PAHX ablate its role in the metabolism of phytanoyl CoA, and results in the accumulation of phytanic acid, which in turn causes symptoms leading to Refsum Disease. The structure and function of PAHX will be discussed and comparisons made with related human enzymes involved in oxygen sensing and signalling roles.