We retrospectively reviewed 100 bone marrow core biopsy specimens from patients with AL (primary) amyloidosis. The morphologic and immunohistochemical features were assessed by standard histochemical stains (H&E, periodic acid-Schiff, Congo red) and immunohistochemical stains for light chain immunoglobulins. Bone marrow core biopsy revealed a plasma cell dyscrasia in 83% (lambda, 65; kappa, 18) of cases. Amyloid deposits were observed in 60% of the bone marrow core biopsy specimens and, when present, were detected most often in blood vessel walls only (39/60). However, if present, interstitial amyloid deposition was significantly more associated with patients with a monoclonal kappa light chain gammopathy (P = .04). Through the careful analysis of standard histochemical and immunohistochemical stains, bone marrow core biopsy provides essential diagnostic information in cases of AL amyloidosis.