The Hospital Management Information System (HMIS) is an essential component in supporting effective, efficient, and high-quality healthcare services. Outpatient satisfaction with services related to HMIS may be influenced by patient characteristics as well as system quality, information quality, and service quality. This study aimed to analyze the factors influencing outpatient satisfaction related to the Hospital Management Information System at Dr. Abdul Rivai Regional General Hospital, Berau, East Kalimantan. This study employed a mixed-methods approach with a sequential explanatory design, in which the quantitative phase was followed by a qualitative phase to provide a deeper understanding of the quantitative findings. The quantitative phase used a cross-sectional design involving 100 outpatients. Data were analyzed using univariate analysis, bivariate analysis with the Chi-Square test, and multivariate analysis using multiple logistic regression. The qualitative phase was conducted through in-depth interviews. The results of the multiple logistic regression analysis showed that system quality and information quality significantly influenced outpatient satisfaction. System quality had a p-value of 0.032 with an odds ratio (OR) of 3.065, while information quality had a p-value of 0.008 with an OR of 4.000. Education was not significantly associated with outpatient satisfaction (p = 0.188; OR = 3.222), and service quality was also not statistically significant (p = 0.520; OR = 1.794). Information quality was identified as the most dominant factor influencing outpatient satisfaction, with an OR of 4.000. In conclusion, patient characteristics, system quality, information quality, and service quality were associated with outpatient satisfaction related to HMIS. Information quality was the most dominant factor. Therefore, Dr. Abdul Rivai Regional General Hospital should improve the quality of information provided through HMIS, particularly in terms of clarity, timeliness, accuracy, comprehensibility, and relevance to patients’ needs.