Factors (demographics, gambling behaviors and comorbid problems) that may be related to the severity of gambling problems were investigated among 440 problem gamblers seeking treatment in an Australian outpatient treatment agency. The participants were divided into sub-threshold pathological gamblers (SPGs; N = 104) and pathological gamblers (PGs; N = 336) using Diagnostic Statistical Manual (DSM) IV diagnosis of pathological gambling. SPGs were more likely to be separated/divorced, while PGs were more likely to be single. PGs tended to be younger than SPGs. Participation in lottery games was the only form of gambling that could distinguish between the two severity groups. No significant differences were found in participation in more than one gambling session per week and average amount spent per session on various gambling activities between the two groups. PGs were more likely to report financial, relationship, employment, physical, intrapersonal, other excessive behaviors (e.g., substance problems), leisure (e.g., loneliness, boredom) and legal problems than SPGs. Implications and limitations of these findings are discussed.