Human urine is sterile as long as it is in the human body. But is it dirty after leaving the human body? Could you get sick from it, if you drink it or don't wash your hands, for example?
It was believed for a long time that urine stored in the urinary bladder is sterile. However, Wolfe et al(1). recently found evidence of bacterial presence in the urine extracted from bladders of healthy women. In an article just published, Hilt et al. found that at least some bacteria found in the bladder of healthy women are viable and can be grown in a laboratory after extraction from the bladder).2 (Paywall). They expect that the same is the case for men.
From the Hilt et al. paper:
Note that these species for the most part (Actinobaculum being one exception, as a possible uropathogen) appear to be part of the normal microbiome (collection of microorganisms) in healthy people in the same way as bacteria inhabit other parts of healthy persons. Additionally, the recovered organisms required special care to achieve growth:
Thus, fresh urine is non-sterile but probably unlikely to cause infection in healthy persons.
In the process of leaving the body, there is a chance of contamination from organisms living in the urinary tract or on the surface of the body. However, if organisms picked up from the urinary tract made you sick, I except that you would already be having symptoms of an urinary tract infection, as the stomach is hardly a more forgiving environment. The risk of contamination from the surface of the body would depend on personal hygiene.
See also this question on http://outdoors.stackexchange.com/questions/264/is-drinking-urine-safe
Edit: This might go without saying, but apart from possible pathogens, there are of course other aspects of urine which makes it unfit for general consumption.