The continuous precipitation of silver nanoparticles was performed at room temperature using sodium borohydride (NaBH4) as the reducing agent. The effects of the concentration of the silver precursor (i.e., silver nitrate), the quantity of dispersing polymer [poly(vinyl pyrrolidone), PVP], and the flow rates of the reacting solutions on the resulting particle size and its distribution were investigated and are reported herein. Particles with average sizes ranging from 13 to 130 nm were obtained. Our results show that there is an optimal flow rate for each precursor concentration to obtain a uniform size distribution of the silver nanoparticles. This phenomenon can be explained in terms of the sequence of mixing, reaction, supersaturation generation and subsequent nucleation, growth, and agglomeration steps. Size control was mainly achieved through the use of PVP/AgNO3 weight ratios ranging from 0.05 to 1.5. Other properties such as residual PVP quantity and boron and sodium contamination are also reported here for several representative samples.