Giant cell arteritis (GCA) and Takayasu arteritis (TAK) have been considered distinct disorders based on their clinical features, age of onset, and ethnic distribution. However, on closer examination, these disorders appear more similar than different. The histopathology of arterial lesions in these diseases may be indistinguishable. Imaging studies have revealed large vessel inflammation in at least 60% of patients with GCA. We questioned whether the distinctions between these diseases might in part be an artifact due to bias in gathering historical and physical data. We postulated that signs and symptoms of GCA and polymyalgia rheumatica occur in patients with TAK but have been under-reported as a result of this bias.We performed a retrospective review of 75 patients with TAK and 69 patients with GCA (per American College of Rheumatology criteria). Signs and symptoms attributable to disease within the year before and following diagnosis, treatment and interventional outcomes, and mortality were recorded using a standardized database. All cases were evaluated by a single physician, using identical history and physical examination forms for patients with both diseases.Patients were predominantly female (TAK 91%, GCA 82%) and white (TAK 88%, GCA 95%). New headache was a presenting symptom in 52% of TAK and in 70% of GCA patients. All TAK patients underwent vascular imaging studies and were demonstrated to have large vessel abnormalities. However, only a subset of patients with GCA (43/69, 62%) was similarly studied. Among this group, 73% of GCA patients had at least 1 arterial lesion identified. In both TAK and GCA, the most common sites of involvement were the aorta (TAK 77%, GCA 65%) and subclavian (TAK 65%, GCA 37%) arteries. Compared to patients with TAK, patients with GCA had a greater prevalence of jaw claudication (GCA 33%, TAK 5%), blurred vision (GCA 29%, TAK 8%), diplopia (GCA 9%, TAK 0%), and blindness (GCA 14%, TAK 0%).Symptoms, signs, and imaging abnormalities that are characteristic of GCA or TAK are often present, albeit in differing frequencies, in both disorders. These findings lend support to the hypothesis that these diseases may not be distinct entities, but represent skewed phenotypes within the spectrum of a single disorder. Differences in frequencies of manifestations may reflect a significant bias in how data are gathered for patients with each disease, as well as the influence of vascular and immunologic senescence.