It is unclear if surveillance bias (increased reports to Child Protective Services [CPS] related to program involvement) has a substantial impact on evaluation of home visiting (HV) prevention programs. We estimated surveillance bias using data from Connecticut's HV program, birth certificates, CPS, and hospitals. Using propensity score matching, we identified 15,870 families similar to 4015 HV families. The difference-in-differences approach was used to estimate surveillance bias as the change in investigated reports from the last 6 months of program involvement to the next 6 months. The median age of the children at program exit was 1.2 years (range: 60 days, 5 years). We estimated that 25.6% of investigated reports in the HV group resulted from surveillance bias. We reviewed CPS reports of 194 home-visited families to determine if a home visitor made the report and found that 10% were directly from home visitors. Program evaluations should account for surveillance bias.