• A multilevel model reviewing four assessment levels for pediatric serum drug concentrations was developed. Criteria for appropriate indication, sample collection, documentation, and utilization were based on therapeutic drug monitoring principles. The model was applied to 222 pediatric serum drug concentrations. Inadequate documentation was a major problem, but it occurred at a lower rate (37%) than previously reported. The rates of inappropriateness for indication (15%), sample collection (16%), and utilization (10%) were well within reported ranges but were significantly lower with pharmacy input. Overall, 48.2% of drug concentrations were inappropriate. Digoxin, phenobarbital, and aminoglycosides had the highest error rates. The annualized cost of inappropriate serum drug concentrations was $12 325. The described method allows for targeting of educational programs with defined areas for improvement. The findings of this study also support the involvement of clinical pharmacists in the therapeutic drug monitoring process.