To the Editor I write to address an error in the Research Letter “A Difference-in-Differences Analysis of Youth Smoking and a Ban on Sales of Flavored Tobacco Products in San Francisco, California” that was published Online First on May 24, 2021, and in the August 2021 issue of JAMA Pediatrics.1 I had reported that the data from the 2019 Youth Risk Behavior Surveillance System (YRBSS) survey wave were collected during the spring semester after the ban on flavored tobacco sales was implemented, consistent with published descriptions of YRBSS surveys as generally fielded in the spring.2 However, this time period was incorrect. In March 2022, I was informed that data from the 2019 wave of the San Francisco district YRBSS survey were collected between November 5, 2018, and December 14, 2018, which was after the ban’s legal effective date (July 21, 2018) and amid retailer outreach, education, and initial compliance checks but before the San Francisco Department of Public Health began enforcing penalties for noncompliance (scheduled for January 1, 2019, but ultimately delayed3). Clarification of this information to note the timing of the survey wave and dates the ban legally took effect does not change the overall findings of this analysis. The clarified findings are as follows: “Comparing recent smoking rates by wave revealed similar trends in San Francisco vs other districts in the 2011-2017 waves but subsequent divergence in the 2019 survey wave…”1 and “…San Francisco’s partially implemented flavor ban was associated with higher odds of recent smoking among underage high school students relative to concurrent changes in other districts...”1