Introduction: The calculation and application of weights is an important step in producing estimates from a sample survey. Practical applications of survey weighting requires a number of decisions on how to handle issues, such as extreme weights and small cell sample sizes. This paper aims to identify diagnostics that may assist in making decisions about aggregation of small cells and trimming of extreme weights, using a case study where there is high variability in the survey weights due to the survey design. Method: Approximately 80 hospitals, ranging from tertiary teaching hospitals to small local hospitals, are included in the New South Wales (NSW) Emergency Department survey. Unbiased estimates are required for each hospital, as well as for 16 administrative areas and for NSW. Several options for modifying the weights were applied. Results: Results show the effect of the options on results for key variables at all three reporting levels (hospital, area, NSW). Diagnostics were identified that can help inform decisions about trimming and aggregation of cells. Conclusion: Simple diagnostics can be used to assist in the decision-making about how to modify weights.