The development of additive ('If only I had done...') and subtractive ('If only I had not done') counterfactual reasoning was examined in children with High Functioning Autism Spectrum Disorders (HFASD) (n = 72) and typically developing controls (n = 71), aged 6-12 years. Children were presented four stories where they could generate counterfactuals based on a given consequent (e.g., 'you left muddy footprints in the kitchen. How could that have been prevented?'). Children with HFASD increasingly used subtractive counterfactuals as they got older, but controls showed an increase in additive counterfactuals, which may be linked to their growing adaptive and flexible skills. Children with HFASD likely develop different strategies for their counterfactual reasoning. The role of IQ and ideational fluency will be discussed.