Aims: This study aims to explore possible associations between self-efficacy and healthcare and drug expenditures (i.e. direct costs) in patients with chronic heart failure (CHF) or chronic obstructive pulmonary disease (COPD) in a study investigating the effects of person-centred care delivered by telephone. Methods and results: This exploratory analysis uses data from an open randomized controlled trial conducted between January 2015 and November 2016, providing remote person-centred care by phone to patients with CHF, COPD, or both. Patients hospitalized due to worsening of CHF or COPD were eligible for the study. Randomization was based on a computer-generated list, stratified for age ≥ 75 and diagnosis. At a 6 month follow-up, 118 persons remained in a control group and 103 in an intervention group. The intervention group received person-centred care by phone as an addition to usual care. Trial data were linked to register data on healthcare and drug use. Group-based trajectory modelling was applied to identify trajectories for general self-efficacy and direct costs. Next, associations between self-efficacy trajectories and costs were assessed using regression analysis. Five trajectories were identified for general self-efficacy, of which three indicated different levels of increasing or stable self-efficacy, while two showed a decrease over time in self-efficacy. Three trajectories were identified for costs, indicating a gradient from lower to higher accumulated costs. Increasing or stable self-efficacy was associated with lower direct costs (P = 0.0013). Conclusions: The findings show that an increased or sustained self-efficacy is associated with lower direct costs in patients with CHF or COPD. Person-centred phone contacts used as an add-on to usual care could result in lower direct costs for those with stable or increasing self-efficacy.