BACKGROUND & AIMS: Gambling disorder (GD) may have its onset in a wide range of ages, from adolescents to old adults. In addition, individuals with GD tend to seek treatment at different moments in their lives. As a result of these characteristics (variable age at onset and variable age at treatment seeking), we find subjects with diverse duration of illness (DOI) in clinical practice. DOI is an important but relatively understudied factor in GD. Our objective was to investigate clinical and neurocognitive characteristics associated with different DOI. METHODS: This study evaluated 448 adults diagnosed with GD. All assessments were completed prior to treatments being commenced. RESULTS: Our main results were: (a) there is a negative correlation between DOI and lag between first gambling and onset of GD; (b) lifetime history of alcohol use disorder (AUD) is associated with a longer duration of GD; (c) the presence of a first-degree relative with history of AUD is associated with a more extended course of GD; and (d) there is a negative correlation between DOI and quality of life. DISCUSSION: This study suggests that some important variables are associated with different DOI. Increasing treatment-seeking behavior, providing customized psychological interventions, and effectively managing AUD may decrease the high levels of chronicity in GD. Furthermore, research on GD such as phenomenological studies and clinical trials may consider the duration of GD in their methodology. DOI might be an important variable when analyzing treatment outcome and avoiding confounders.