The broad definition of "elder abuse" used for this study included domestic physical abuse, exploitation, neglect, sexual abuse, abandonment, emotional abuse, and any other categories defined in a State's statutes or regulations. A questionnaire was mailed to 1,763 adult protective service (APS) office investigators in 44 States and the District of Columbia. A total of 1,409 completed questionnaires were returned (80-percent return rate). The questionnaire queried the APS's about investigative structures and techniques for elder abuse and also requested elder-abuse case data for 1999. The study found that elder-abuse reports to APS offices ranged from 0 to 191.7 per 1,000 elder population. Investigation and substantiation rates ranged from 0 to highs of 150.0 and 116.7, respectively. Investigation rates for elder abuse were higher in counties that had investigators assigned to investigate only elder-abuse cases, in counties with investigators who had social work backgrounds, and in counties with investigators who reported that elderly victims of abuse were better off after investigations. Longer training programs for investigators was associated with high substantiation rates. The study concludes that elderly victims of abuse are best served when investigators with social work education and experience are given specialized training to deal only with cases of elder abuse. 3 tables, 1 figure, and 15 references