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.