Objective The aim of this study was to identify the drug-related problems and drug-drug interactions (DDIs) among the inpatients admitted to an internal medicine ward. Method A prospective, exploratory study was planned and all the prescriptions of inpatients admitted to the internal medicine department from 10 to 24 April 2011 were assessed at a public hospital in Alahsa, Saudi Arabia. Descriptive analysis was performed for sociodemographic aspects of the patients. Prescriptions of the studied population were compiled both for potential drug interactions and number of cases in each class of 'nature of interaction'. All the analysis was performed using SPSS v.18. Key findings Total number of records reviewed during this period was 57. Among these 57 cases, 104 interactions were found. On an average 2 to 11 drugs were prescribed per prescription. In our study, we found that out of the total 104 DDIs, 9 (8.5%) DDIs were serious in nature while the major proportion (69.0%) of the interactions was also significant. It was noticed that the significant DDIs were found associated with the number of drugs (χ 2 = 10.992, degree of freedom (df) = 9, P = 0.002*) and age (χ 2 = 5.494, df = 1, P = 0.019*) of the patients. Conclusion Findings of the current study revealed a high occurrence of DDIs. Number of drugs, age and number of comorbid medical conditions are some of the factor demonstrating a possible association with the DDIs. Patients with cardiovascular disorders were found more prone to one or more DDIs.