Background: Surveillance PET imaging following curative intent treatment of non-small cell lung cancer (NSCLC) or colorectal cancer (CRC) is not supported by available evidence. ASCO and ABIM's joint Choosing Wisely campaign recommends against surveillance PET, yet the frequency with which PET imaging is performed during surveillance care is unknown. Methods: 65,748 patients age 66+, diagnosed with stage I-IIIA NSCLC or Stage I-III CRC in 2001-2009, who underwent surgical resection were identified in SEER-Medicare data. Eligibility for surveillance started 180 days post-operatively. Use of imaging was assessed during the first year of surveillance and classified as 1) Any PET: receipt of PET or PET/CT regardless of other imaging, or 2) PET-only: receipt of PET or integrated PET/CT only, in patients who did not undergo separate dedicated CT imaging. Unadjusted proportions of patients receiving each category of surveillance were calculated by cancer type, diagnosis year, and stage. Equality of proportions was assessed between diagnosis years with ANOVA tests. Results: 7,393 NSCLC patients and 35,050 CRC patients met inclusion criteria. PET use more than doubled over the study period in both cohorts. 11% of all NSCLC patients diagnosed in 2001 received any PET vs. 25% diagnosed in 2009 (P < 0.001). Similarly, 4% of all CRC patients diagnosed in 2001 received any PET vs. 12% diagnosed in 2009 (P < 0.001). PET utilization was more common in higher stage NSCLC and CRC patients, and increased significantly between 2001 and 2009. In Stage IIIA NSCLC patients diagnosed in 2001, 15% received any PET compared to 42% diagnosed in 2009 (P = 0.015). In this same group of patients, 1.5% diagnosed in 2001 received PET-only, compared to 15% diagnosed in 2009. Among Stage III CRC patients any PET use increased from 9% for those diagnosed in 2001 to 27% for those diagnosed in 2009 (P < 0.001), while use of PET-only increased from 1% to 8% over the same period (P < 0.001). Conclusions: Although not indicated in surveillance, PET utilization has more than doubled among NSCLC and CRC survivors over the study period. While surveillance rates may be increasing generally, increased rates of PET-only imaging suggest PET is inappropriately replacing existing surveillance protocols.