Aims and objectives. To explore the experience of self-managing medication among older people with multimorbidity. Background. Older people with multimorbidity are now more likely to live at home and to self-medicate. Reduced assistance from professional caregivers is associated with medical errors. Design. Face-to-face interviews were conducted with older people with multimorbidity. Methods. Participants aged >= 75 years with >= 2 medical diagnoses and living at home or in special accommodation were interviewed. Twenty-eight men and women (mean age 84 years) participated. Interviews lasted from 45 minutes-2 hours and were transcribed verbatim. A lifeworld-based phenomenological method was used for analysis. Results. Uncertainty among the participants increased with their experience of side effects and concern that the medication might be harmful. These uncertainties were reinforced by a fear of malpractice when several physicians were involved. This meant living with ambivalence when taking the medication, which required a trade-off between symptom relief and reducing side effects. A lack of continuity with physicians and nurses led to uncertainty in maintaining an overview of the medications. By contrast, when the relationships were supportive and caring, the uncertainties diminished. Four concepts were used to describe the various meanings of this experience: adapting to a new lifestyle; ambivalence towards medicine; experience of side effects and concerns about medical errors; and relationships as sources of feeling secure. Conclusions. Medications can cause side effects, and unclear benefits increase the uncertainty for older people with multimorbidity. Health care professionals need to develop an understanding of each patient's experience of such uncertainty. Relevance to clinical practice. Health care professionals can give support and show understanding for older people's existential uncertainty by creating good relationships and continuity in care, and offering appropriate information. Regular visits should be scheduled to manage any problems patients might have when self-medicating.