The diastereomeric composition of hexabromocyclododecane (HBCD) in eggs of peregrine falcon (Falco peregrinus), white-tailed sea eagle (Haliaeetus albicilla), guillemot (Uria aalge) and common tern (Sterna hirundo) as well as the guillemots' main prey, herring (Clupea harengus) was determined by reversed-phase chromatography with triple-stage quadrupole mass spectrometric detection (LC-MS-MS). alpha-HBCD was the predominant diastereomer in all bird species, while in herring, gamma-HBCD made a substantial contribution. Two, as yet unidentified diastereomers, were detected in common tern egg. The alpha-, beta- and gamma-HBCD (+) and (-) enantiomers were separated using a chiral stationary phase. The enantiomer fractions for alpha-HBCD differed substantially between different bird species as well as between guillemot and its prey, herring. Total HBCD levels determined by LC-MS-MS were comparable to those previously obtained by GC-MS.