BACKGROUND AND AIMS: Due to their small sample sizes, geographic specificity and limited examination of socio-demographic characteristics, recent studies of methamphetamine use among people using heroin in the United States are limited in their ability to identify national and regional trends and to characterize populations at risk for using heroin and methamphetamine. This study aimed to examine trends and correlates of methamphetamine use among heroin treatment admissions in the United States. DESIGN: Longitudinal analysis of data from the 2008 to 2017 Treatment Episode Data Set. Descriptive statistics, trend analyses and multivariable logistic regression were used to examine characteristics associated with methamphetamine use among heroin treatment admissions. SETTING: United States. PARTICIPANTS: Treatment admissions of people aged ≥ 12 years whose primary substance of use is heroin. MEASUREMENTS: Primary measurement was heroin treatment admissions involving methamphetamine. Secondary measurements were demographics of sex, age, race/ethnicity, US census region, living arrangement and employment status. FINDINGS: The percentage of primary heroin treatment admissions reporting methamphetamine use increased each year from 2.1% in 2008 to 12.4% in 2017, a relative percentage increase of 490% and an annual percentage change (APC) of 23.4% (P < 0.001). During the study period, increases were seen among males and females and among all demographic and geographic groups examined. Among primary heroin treatment admissions reporting methamphetamine use in 2017, 47.1% reported injecting, 46.0% reported smoking, 5.1% reporting snorting and 1.8% reported oral/other as their usual route of methamphetamine use. CONCLUSIONS: Methamphetamine use among heroin treatment admissions in the United States increased from one in 50 primary heroin treatment admissions in 2008 to one in 8 admissions in 2017.