2-Aminoadamantane-2-carboxylic acid hydrobromide crystallizes in space group P21/c with a= 6.40, b= 11"62 and c= 15.38 ,~, fl= 95.2 °, Z=4. The structure was solved by the heavy-atom method with 1484 visual reflexions and refined to an R of 0.097. The substitution of the amino and the carboxyl group at C(2) of the adamantane does not significantly affect its highly symmetric cage-hke structure.In relation to amino acid structures, a rare occurrence of the C(11)-O(2) double bond trans to the nitrogen N about the C(2)-C(11) bond is observed in this structure. The nitrogen atom lies 1.07 A oat of the plane containing the carboxyl group and C(2).