The insect sex peptide (SP) elicits a variety of biological responses upon transfer to the mated female. SP contains 36 amino acids, including a tryptophan-rich N-terminal region, a central region containing five hydroxyproline (Hyp) residues, and a C-terminal region enclosed by a disulfide bridge. The solution structure of SP, studied here using NMR spectroscopy, includes a motif WPWN that adopts a type I β-turn in the N-terminal Trp-rich region. This turn region is connected to the central Hyp-rich region, which adopts extended and/or PPII-like conformations. The C-terminal disulfide-bonded loop populates helical turns or nascent helical structure. Overall, the results reveal a rather flexible peptide that lacks a compact folded structure in solution.