Background: Longitudinal, patient-centered care represents a challenge for general practitioners (GPs), and in this context, reminder systems can offer targeted support. This study aimed to identify details of such reminders: (1) contents of care addressed, (2) their mode of display in the electronic health record (EHR), (3) their visual appearance, (4) personnel responsibilities for editing and applying reminders, and (5) use of reminders for patient recall. Methods: This mixed-methods study comprised (1) a cross-sectional survey among 185 GP practices from a German university network, and (2) structured observations of reminder utilization in six practices based on a clinical vignette describing a multimorbid senior with 26 care needs. Descriptive statistics were performed for survey data. The practice observations were analyzed by portraying different types of reminders. Results: Seventy-three of 185 practices completed the survey (39.5%): 98.6% reported using reminders in the EHR. Frequent care contents addressed were allergies/adverse drug events (95.8%), preventive measures (93.1%), participation in disease management programs (87.5%), chronic diseases (75.0%), and upcoming vaccinations (68.1%). Practice observations showed a variety of mainly self-configured reminders. In a patients' EHR, information was displayed (1) compiled in a separate field, (2) scattered throughout the EHR, and/or (3) in a pop-up window. The visual appearance of electronic reminders varied: (1) colored fields with short text, (2) EHR entries and/or billing codes in pre-defined colors, (3) abbreviations within the treatment documentation, (4) symbols within the treatment documentation, (5) symbols linked to free text fields, and (6) traffic light schemes. Five practices self-designed reminders 'as needed'; one practice applied an EHR-embedded, pre-defined reminder system. Practices used reminders for a mean of 13.3 of the 26 aspects of care detailed in the clinical vignette (range: 9-21; standard deviation (SD): 4.3). Practices needed 20-35 min (mean: 27.5; SD: 6.1) to retrieve the information requested. Conclusions: Most GP practices use self-designed, visual reminders for some aspects of care, yet data-based, sophisticated solutions are needed to improve longitudinal care.