The objective of this study was to estimate the health service use and costs resulting from the introduction of the interRAI Minimum Data Set-Home Care (MDS-HC) assessment compared with usual assessment.A randomised controlled trial of elderly people in New Zealand measured the use and cost of prescribed and delivered (4 months post-assessment) health services of 153 participants assessed using the standard [Needs Assessment and Service Co-ordination (NASC)] tool,and 158 participants assessed using the MDS-HC. The results suggest that the MDS-HC resulted in more prescribed personal health and community services, and less disability support services than with NASC. The cost of prescribed services was significantly greater for the MDS-HC (NZ$1840) than the NASC (NZ$1522, P < 0.001). The cost of delivered services was significantly greater for the MDS-HC (NZ$4809)than the NASC (NZ$2727, P < 0.001), including higher costs of hospitalizations (NZ$2523 vs. NZ$1112, P= 0.257). There were pronounced differences among 'low-need' compared with 'high-need'elderly people. These results suggest that the interRai assessment tool resulted in greater cost of prescribed preventive services and less prescribed disability services than the NASC. However, differences in delivered services were driven primarily by differences in hospitalizations. The results highlight the importance of integrating the assessment procedure with the delivery of health services, but suggest that further study is warranted. The results have implications for purchasers of health services for elderly people.