The Food and Drug Administration approved pre-exposure prophylaxis (PrEP) to prevent HIV infection, and the Centers for Disease Control and Prevention has presented PrEP as a prevention option for groups at high risk such as men who have sex with men (MSM). Intervention data provide some information on how PrEP affects sexual behavior of MSM in trials, open label extensions, or clinics. However, it is unclear whether sexual risk and preventive behavioral patterns are changing in the population as a whole as PrEP becomes more widely available, whether due to PrEP use or other factors. We examined trends in PrEP use, numbers of condomless anal sex partners, consistent condom use, and seroadaptive strategies in San Francisco-a city which has actively promoted PrEP-using data from National HIV Behavioral Surveillance (NHBS). NHBS recruited 1211, 383, 373, and 268 HIV-negative MSM in 2004, 2008, 2011, and 2014, respectively. PrEP use increased from zero in 2004, 2008, and 2011 to 9.6 % in 2014. The proportion of men with no condomless anal sex partners dropped from 60.6 % in 2004, to 58.2 % in 2008, to 54.2 % in 2011, to 40.2 % in 2014. Consistent condom use decreased from 36.8 % in 2004, and 30.5 % in 2008 and 2011, to 18.3 % in 2014. PrEP's introduction and scale-up enters in a pre-existing trend of decreasing condom use and increasing sexually transmitted infections among MSM which may be accelerating in recent years. While PrEP use should be scaled up as a prevention option among those who would benefit most, we believe that public health officials need to be realistic about the possibility that condom use could very well continue to decline as PrEP use increases, and to an extent that may not be directly or indirectly offset by PrEP.