The treatment of complex coronary lesions with conventional balloon angioplasty is associated with a reduced success rate and an increased incidence of complications. To evaluate the influence of lesion morphology on the outcome of coronary excimer laser angioplasty, morphologic parameters of 148 target lesions in 147 consecutive patients were determined. Morphologic analysis included target vessel, involved vessel segment, vessel diameter, minimal lumen diameter, length of the lesion, single discrete (concentric/eccentric) or complex lesions (occlusions, bifurcational, tandem or long segmental lesions), American College of Cardiology/American Heart Association Task Force classification, lesion location in curved or straight vessel segments, prestenotic vessel tortuosity and the direction of the laser approach in curved vessels with eccentric lesions. Failure of laser angioplasty occurred in 17 patients because of failed guidewire placement (n = 8), catheter placement (n = 6), or inability to pass the lesion with the laser catheter (n = 3). Successful stand-alone laser angioplasty was achieved in 68 procedures. In 63 interventions additional balloon angioplasty was necessary (n = 60) or stand-alone laser angioplasty was not successful (n = 3). The frequency of complex lesions, particularly total occlusions (p less than 0.001) and prestenotic vessel tortuosity (p = 0.002) was significantly increased in the group with failed laser attempts. Statistical analysis of the morphologic parameters in successful stand-alone laser interventions compared with combined or unsuccessful interventions revealed no significant difference. These data suggest that failure of laser angioplasty occurs because of low catheter flexibility and the need for guidewire support in treating totally occluded vessels.(ABSTRACT TRUNCATED AT 250 WORDS)