In Icelandic pedigrees a cystatin C mutation, glutamine 68 (L68Q), causes autosomal dominant cerebral amyloid angiopathy-related hemorrhage (CAAH). We examined 33 patients with sporadic CAAH for this mutation. None carried L68Q and, including this report, only one of 52 published cases of sporadic CAAH has had the cystatin C mutation. Despite vascular colocalization of cystatin C with amyloid beta-protein, cystatin C L68Q is rare in sporadic CAAH.