We determined the clinical and sociodemographic predictors of beginning active treatment in an ethnically diverse population of men with low risk prostate cancer initially on observational treatment. We retrospectively studied men diagnosed with low risk prostate cancer between 2004 and 2012 at Kaiser Permanente Northern California who did not receive any treatment within the first year of diagnosis and had at least 2 years of followup. We used Cox proportional hazards regression models to determine factors associated with time from diagnosis to active treatment. We identified 2,228 eligible men who were initially on observation, of whom 27% began active treatment during followup at a median of 2.9 years. NonHispanic black men were marginally more likely to begin active treatment than nonHispanic white men independent of baseline and followup clinical measures (HR 1.3, 95% CI 1.0-1.7). Among men who remained on observation nonHispanic black men were rebiopsied within 24 months of diagnosis at a slightly lower rate than nonHispanic white men (HR 0.70, 95% CI 0.6-1.0). Gleason grade progression (HR 3.3, 95% CI 2.7-4.1) and PSA doubling time less than 48 months (HR 2.9, 95% CI 2.3-3.7) were associated with initiation of active treatment independent of race. Sociodemographic factors such as ethnicity and education may independently influence the patient decision to pursue active treatment and serial biopsies during active surveillance. These factors are important for further studies of prostate cancer treatment decision making.