Background: The 585-nm flashlamp-pumped pulsed-dye laser (PDL) has proven to be the treatment of choice for certain keloids and hypertrophic scars, but the precise fluence, numbers of treatment, and treatment interval remain anecdotal. Objective: This study was performed to determine whether the therapeutic outcome of the PDL varies with the energy density (fluence) of the laser pulses and numbers of treatment. Method: Ten previously untreated, erythematous, keloidal or hypertrophic median sternotomy scars of 10 patients were divided into 4 segments and were randomly treated with a 585-nm PDL at a fluence of 3, 5, and 7 J/cm² to 3 of 4 segments every 4 weeks for a total of 6 treatment sessions. One segment of each patient's scars was untreated and served as a control. Clinical improvement including scar height, erythema, and pliability was evaluated before treatment and every 8 weeks for a total period of 32 weeks. Self-assessment was also determined by patients on a 25% increment of improvement scale comparing week 0 and week 32. Results: A significant improvement in scar height, erythema, and pliability was noted in all laser-treated scar areas. There was no significant difference in treatment outcome versus the fluence of the laser (3, 5, and 7 J/cm²), although there was a trend for lower fluences to show more improvement. Objective clinical improvement was seen as early as week 16, after more than two treatments were given. Multiple treatments (>2) appeared to provide a greater percentage of scar resolution. Conclusions: The clinical improvement of scars after PDL treatment demonstrates no statistically significant fluence dependence in this study, but a trend toward better response with lower fluences is seen. In addition, multiple treatment sessions are suggested for achieving greater response. (J Am Acad Dermatol 2001;45:557-65.)