The Japanese government actively urges pharmacists to support efforts to reduce surplus medicines. However, these activities currently serve only to dispose of surplus medicines; no measures are being taken to fundamentally prevent the accumulation of surplus medicines from the outset. A deep understanding of patients' views about storing medicines at home and how they might be accumulating surplus medicines would contribute to the prevention of surplus accumulation. This study aimed to characterize the process by which elderly chronic disease patients in Japan accumulate surplus medicines. Semi-structured interviews were conducted with 18 elderly patients, and the interview data were analyzed using a modified grounded theory approach (M-GTA) to present the process by which surplus medicines were accumulated at patients' homes. The results suggest that elderly patients with chronic diseases often wish to avoid unnecessary medications because of anxiety about medicines, and that these patients seek to maximize medicine suppression. In this context, patients use their own judgment to decide whether to use medicines as needed. Additionally, when patients accumulate surplus medicines, they hesitate to throw them away because they feel that to do so is mottainai (wasteful), or because they accumulate surplus medicines as emergency household medicines. These findings reveal when and how surplus medicine accumulation occurs and the points at which pharmacists can easily intervene to promote a close relationship with patients.