The formation of NOx during solid fuel or waste combustion is a very complex process, making it particularly difficult to accurately estimate NOx emissions. The main purpose of the present study was to develop a correlation between the composition of a solid fuel or (mixed) waste and the fuel-NOx emissions from its combustion, allowing accurate prediction of NOx emissions from incineration processes, useful for assessing the environmental impact. Literature was scanned for relevant and complete data sets concerning different solid fuel or waste types, incinerated in specific types of incinerators. Previously reported correlations showed a linear relationship between the conversion of fuel-N to NO and the O/N and H/N weight ratio, deduced from the element composition of a solid fuel. The overall fitting of the collected data sets in terms of these ratios is, however, rather poor. Considerations of both the element composition of the fuel, and the functional form of the fuel-N lead to the conclusion that for all data sets a good linear correlation existed between a single weight ratio, the CH/N ratio, and the conversion of fuel-N to NO. (C) 2011 Elsevier Ltd. All rights reserved.