Few studies have examined the prevalence of problem and pathological gambling among clients of homeless service agencies. The objective of this study was to estimate the prevalence of problem gambling among these clients. We collected primary data on gambling using the NORC diagnostic screen for disorders. Using a modified time-location recruitment approach 264 clients of a community homeless service agency were screened for lifetime gambling problems. Descriptive statistics were produced using SPSSX. The prevalence of lifetime problem gambling was 10 % and that of pathological gambling was 25 % in this sample. The prevalence of lifetime problem and pathological gambling was alarmingly high relative to the general population lifetime prevalence. Better insight into interventions for gambling that might reduce risk of homelessness will help service agencies gauge the needs of their clients and to implement change to service delivery and screening practices.