To assess the impact of gambling above the low-risk gambling limits developed by Currie et al. (2006) on future harm. To identify demographic, behavioural, clinical and environmental factors that predict the shift from low- to high-risk gambling habits over time. Design: Longitudinal cohort study of gambling habits in community-dwelling adults. Setting: Alberta, Canada. Participants: A total of 809 adult gamblers who completed the time 1 and time 2 assessments separated by a 14-month interval. Measurements: Low-risk gambling limits were defined as gambling no more than three times per month, spending no more than CAN$1000 per year on gambling and spending less than 1% of gross income on gambling. Gambling habits, harm from gambling and gambler characteristics were assessed by the Canadian Problem Gambling Index. Ancillary measures of substance abuse, gambling environment, major depression, impulsivity and personality traits assessed the influence of other risk factors on the escalation of gambling intensity. Findings: Gamblers classified as low risk at time 1 and shifted into high-risk gambling by time 2 were two to three times more likely to experience harm compared to gamblers who remained low risk at both assessments. Factors associated with the shift from low- to high-risk gambling behaviour from time 1 to time 2 included male gender, tobacco use, older age, having less education, having friends who gamble and playing electronic gaming machines. Conclusions: An increase in the intensity of gambling behaviour is associated with greater likelihood of future gambling related harm in adults.