Although isolated foci of arteritis ("skip lesions") are presumed to occur in temporal arteritis, there is little documentation of their existence or significance. We have identified skip lesions in 17 of 60 patients (28%) with temporal arteritis, based on a retrospective and prospective examination of temporal artery biopsy specimens. By examining more than 6,000 serial sections of arteries from patients with skip lesions, we have found foci or arteritis as short as 330 mu in length in an otherwise normal biopsy specimen. Our study emphasizes the need to biopsy long segments of artery, to examine multiple histologic sections, and to perform a contralateral temporal artery biopsy when frozen-section examination of the first side is normal.