The use of blood pressure cuffs containing bladders of appropriate size for the arm is a known prerequisite for correct blood pressure measurements. The Tricuff, containing three inflatable bladders of varying dimensions, one of which is automatically selected to fit the arm circumference, was compared to a standard cuff (12 x 35 cm) in 137 persons. In persons with large arms (circumference > or = 32 cm) measurement with the Tricuff showed on average 19.2 mm Hg lower systolic pressure and 12.9 mm Hg lower diastolic pressure than with the standard cuff. In persons with small arms (< 32 cm) the corresponding differences were 9.0 mm Hg and 7.5 mm Hg. Compared to the Tricuff, the standard cuff overestimates blood pressure in people with a large arm circumference. Overestimation may also be caused by the rubber bladder bulging more from below the standard soft nylon cuff than what the firmer texture of the Tricuff allows, resulting in falsely high values even in persons with normal arm circumference.