Summary Background The pulsed-dye laser (PDL) is the treatment of choice for port-wine stains (PWS). Multiple treatments are usually necessary, with standard treatment intervals ranging between 6 and 12 weeks. However, there are no studies on the effect of treating PWS at different time intervals, and the ideal time interval between treatments has not yet been agreed. It is uncertain whether treatment is more effective if administered at shorter time intervals. Objectives To establish whether the treatment of PWS with the variable pulse width 595-nm (V-beam®) PDL at 2-week intervals achieves better results, with no difference in the complication rate, than treatment given at 6-week intervals. Methods We prospectively investigated 15 patients with PWS. Each patient had the whole PWS treated at initial visit. Half of the PWS was randomly allocated to be treated at 2 weeks and the other half at 6 weeks from initial visit. Both halves of the PWS thus were treated twice in total, once at the initial visit and the second treatment either at 2 weeks or 6 weeks from initial visit. At 12 weeks an observer blinded to treatment allocation clinically evaluated the results. The outcome measure was lightening of the PWS as measured with a reflectance spectrophotometer. Complications were recorded throughout the study period. Results Of the 15 patients, 13 completed the study. Three patients had two PWS each treated separately, giving a total of 16 treated PWS sites. In 11 sites (69%), the 2-week interval treatment resulted in greater reduction in reflectance than the 6-week interval treatment. Using the nonparametric Wilcoxon matched-pair signed rank test, the 2-week treatment interval site resulted in greater reduction in reflectance measurements compared with the 6-week treatment interval site (P < 0·01). This agreed closely with independent observer assessment judging that the 2-week treatment interval resulted in better lightening of the PWS than the 6-week treatment interval (P = 0·003). There were no adverse reactions from the treatments. Conclusions Preliminary data suggest that a treatment interval of 2 weeks is well tolerated by patients and resulted in greater lightening of the PWS in the majority, compared with a standard 6-week interval. It also has the potential to reduce the total duration of a course of treatment significantly.