OBJECTIVE To assess whether and to what extent irrigation fluid absorption occurs during laser vaporization (LV) of the prostate using the 180 W XPS™ GreenLight laser. METHODS This prospective investigation was performed in a tertiary care center with a consecutive series of patients undergoing 180 W LV of the prostate. Intraoperative irrigation was performed with isotonic saline containing 1 % ethanol. The volume of irrigation fluid absorption was calculated from periodically performed breath ethanol measurements during LV. Additionally, intraoperative changes in biochemical and hematological blood parameters were assessed. RESULTS Positive breath ethanol tests were detectable in 22 of 54 patients. The median absorption volume in these patients was 950 ml (range 208-4579 ml). Ten patients absorbed more than 2000 ml. Absorbers had smaller prostates, more capsular perforations and injuries to venous sinuses, and more total energy was applied with higher output power. Five patients had transient symptoms potentially related to fluid absorption. A significant drop in hemoglobin, hematocrit, venous pH and bicarbonate and an increase in chloride were detectable in the absorber group. These changes were significantly different in the non-absorber group. CONCLUSIONS Absorption of irrigation fluid did occur in a relevant proportion of patients undergoing XPS™ GreenLight LV. High-volume absorption (≥2000 ml), which might be clinically relevant, was detectable in almost 20 % of all procedures. Absorption of saline irrigation fluid does not result in a classical TUR syndrome, but fluid and chloride overload can lead to serious complications, particularly in cardiovascular high-risk patients. Thus, patients with symptoms potentially related to fluid absorption should be monitored carefully.