The most common cause of difficulty urinating in men is an enlarged prostate. This is often due to a benign age-related enlargement, but it can also be due to prostate cancer. Difficultly urinating can also be the result of an infection affecting the urinary tract or prostate, according to MedlinePlus.
Difficulty starting or maintaining a stream of urine is relatively common in older men. The difficulty is generally acquired over time. Less common causes of difficulty urinating include trauma or scar tissue along the urinary tract from a previous surgery, according to MedlinePlus. Certain medications may also cause difficulty urinating as a side effect.