Aim To test the strength of the association between parental monitoring trajectories throughout early adolescence (ages 11–14) and gambling behaviours by young adulthood (age 22). Design Longitudinal cohort design. Setting Baltimore, Maryland. Participants The sample of 514 participants with gambling data between ages 16–22 and parental monitoring data between ages 11–14 were predominantly African American and received subsidized lunches at age 6. Measurements The South Oaks Gambling Screen and South Oaks Gambling Screen–Revised for Adolescents collected self‐reports on annual gambling and gambling problems between ages 16–22. The Parental Monitoring Subscale of the Structured Interview of Parent Management Skills and Practices–Youth Version collected self‐reports on annual parental monitoring between ages 11–14. Findings General growth mixture modelling identified two parental monitoring trajectories: (i) ‘stable’ class (84.9%) began with a high level of parental monitoring at age 11 that remained steady to age 14; (ii) ‘declining’ class (15.1%) began with a significantly lower level of parental monitoring at age 11 and experienced a significant to through age 14. The declining class had increased significantly unadjusted (OR = 1.91; 95% CI = 1.59, 2.23; P ≤ 0.001) and adjusted (aOR = 1.57; 95% CI = 1.24, 1.99; P = 0.01) odds of problem gambling compared with non‐gambling. Conclusion Low and/or declining parental monitoring of children between the ages of 11 and 14 is associated significantly with problem gambling when those children reach young adulthood.