The stent delivery system (SDS) is a sheath-covered Palmaz-Schatz stent mounted on a 3.0, 3.5, or 4.0 mm compliant polyethylene balloon catheter; the balloon resists maximal inflation pressures of 5.7, 6.2, or 6.0 atm, respectively. It is postulated that these pressures are too low to obtain optimal stent deployment. Because optimal stent deployment is a prerequisite for optimal short- and long-term outcome, we performed an intravascular ultrasound study to the mode of stent deployment after delivery with the SDS and after high-pressure dilatations with low-compliant, oversized balloon catheters. In 23 patients an intravascular ultrasound study (30 MHz, 4.3F transducer) was performed to the geometry of 29 stents immediately after delivery with the SDS and after successive high-pressure inflations with low-compliant balloons. After delivery with the SDS (3.3 +/- 0.4 mm), stent diameter was 3.0 +/- 0.4 mm. After high-pressure dilatations (12.4 +/- 1.4 atm) with low-compliant balloons (3.9 +/- 0.5 mm), stent diameter increased to 3.4 +/- 0.4 mm (p < 0.001). Only 8 (28%) stents were completely and symmetrically expanded to the corresponding reference diameter with good apposition after delivery with the SDS. Diameter of incomplete deployed stents (n = 16) was 2.8 +/- 0.3 mm. After high-pressure dilatations with low-compliant balloons (3.9 +/- 0.5 mm), diameter increased to 3.4 +/- 0.4 mm (p < 0.001). Now 20 (69%) stents (p = 0.004) became completely and symmetrically expanded to a diameter corresponding to the reference diameter. In conclusion, most stents are suboptimally deployed after delivery with the stent delivery system.(ABSTRACT TRUNCATED AT 250 WORDS)