Adult Protective Services (APS) workers in California investigate complaints of elder abuse and must determine the validity of a complaint with minimal guidelines. It is unclear whether APS workers reach similar conclusions given cases with similar circumstances. To assess variation in case findings and reasons for them, we used data from monthly reports of completed investigations, and investigation outcomes from all 58 California counties from September 2004 to August 2005, telephone interviews with 54 of 58 counties, and site visits to 17 counties. We also compared the data from 2004-2005 with more recent data from 2013. Large variability was found from county to county in the proportions of cases found to be conclusive, inconclusive, and unfounded. The combined analyses revealed significant differences in how individual APS workers interpret definitions of different types of case outcomes, varying skill and experience of the APS workers, individual and county agency factors, and other reasons that influence variability in case findings. Widespread inconsistencies in the outcomes of elder abuse investigations raise issues to be addressed on multiple levels, including the use of APS data for developing policy, standardizing training of APS workers, and seeking just outcomes for the victims of elder abuse