A device and method are provided which achieve tissue ablation as well as tissue coagulation substantially simultaneously during the treatment of BPH by utilizing at least two wavelengths of light. The device and method improve urinary flow and minimize post-treatment blood loss and edema while maintaining a nearly blood-free operating field during treatment by irradiating substantially simultaneously with at least two different wavelengths of light. According to the present invention, tissue ablation is affected by having one wavelength that is highly absorbed in the prostatic tissue while another less highly absorbed wavelength coagulates surrounding tissues while maintaining minimal thermal damage to surrounding tissue. In a preferred embodiment the highly absorbed wavelength is about 1460 nm and the less absorbed by water but with some significant hemoglobin absorption is about 980 nm. This combination aids the patient by reducing blood loss and edema. It can aid the practitioner, especially where imaging is employed, by maintaining a substantially blood-free area during treatment. The present device and method is used in conjunction with optical fibers including side emitting optical fibers to provide a practical, minimally invasive treatment of enlarged prostates.