Abstract 3,4-Dihydroxyphenylacetaldehyde synthase (DHPAAS) catalyzes oxygen-dependent conversion of 3,4-dihydroxyphenylalanine (dopa) to 3,4-dihydroxyphenylacetaldehyde (DHPAA), a likely cross-linking agent precursor of the insect cuticle. In the current study, extensive in vivo experiments in Aedes aegypti show that DHPAAS is essential for abdominal integrity, egg development and cuticle structure formation. Solid-state 13C nuclear magnetic resonance analysis of the Ae. aegypti cuticle molecular structure shows chemical shifts of 115 to 145 ppm, suggesting the presence of catechols derived from DHPAA. The crystal structure of insect DHPAAS was then solved, revealing an active site that is divergent from that of the homologous enzyme dopa decarboxylase. In the DHPAAS crystal structure, stabilization of the flexible 320–350 region accompanies the positioning of the 350–360 loop relatively close to the catalytic Asn192 residue while the conserved active site residue Phe103 adopts an open conformation away from the active center; these distinct features participate in the formation of a specific hydrophobic tunnel which potentially facilitates delivery of oxygen to pyridoxal 5’-phosphate in the conversion of dopa to DHPAA.