Abstract Background The shift of selected surgical procedures from inpatient to outpatient settings has been seen as a solution to improve health care provision. These shifts often occur under pay-for-performance schemes, pay-for-efficiency schemes, or other forms of financial incentives. For this study, we aimed to assess the effect of Decree 132/2009, implemented on February 1, 2009, which increased the relative weights of DRG 60 (“tonsillectomy and/or adenoidectomy, age <18”) performed in outpatient settings, thus acting as a financial incentive. Methods We performed a quasi-experimental study and employed interrupted time series (ITS) and controlled interrupted time series (CITS) designs, using monthly pediatric data provided by The Central Administration of the Health System (ACSS), with discharges between January 2006 and February 2012 (having 37 months pre- and post-decree implementation) of inpatient and outpatient episodes for DRG 60 (affected group) and DRG 163 (“hernia procedures age <18”, the selected control group). We used as study outcomes proportions (number of outpatient episodes divided by the sum of outpatient and inpatient episodes) to quantify increases in outpatient episodes and ratios (number of outpatient episodes divided by the number of inpatient episodes) to quantify decreases in inpatient episodes. Fourier terms were included to adjust for seasonality. Results We obtained statistically significant results only at the trend level for ratios when using the ITS model (0.01574) and for proportions only when using the CITS model (0.00310), although small non-statistically significant increases were obtained for the employed ITS as well as for the CITS design. Conclusions Decree 132/2009, which created financial incentives for the shift from inpatient to outpatient for DRG 60, showed low and non-statistically significant increases using both ITS and CITS models. Key messages • We analyzed the impact of Decree 132/2009 on the pediatric surgeries under DRG 60 performed in outpatient settings in Portugal using interrupted time series and control interrupted time series. • The decree had a small effect at the national level for DRG 60.