The application of already widely available mobile phones would provide medical professionals with an additional possibility of outpatient care, which may reduce medical cost at the same time as providing support to elderly people suffering from chronic diseases, such as diabetes and hypertension. To facilitate this, it is essential to apply user centered development methodologies to counteract opposition due to the technological inexperience of the elderly. In this paper, we describe the design and development of a mobile medical application to help deal with chronic diseases in a home environment. The application is called MyMobileDoc and includes a graphical user interface for patients to enter medical data including blood pressure; blood glucose levels; etc. Although we are aware that sensor devices are being marketed to measure this data, subjective data, for example, pain intensity and contentment level must be manually input. We included 15 patients aged from 36 to 84 (mean age 65) and 4 nurses aged from 20 to 33 (mean age 26) in several of our user centered development cycles. We concentrated on three different possibilities for number input. We demonstrate the function of this interface, its applicability and the importance of patient education. Our aim is to stimulate incidental learning, enhance motivation, increase comprehension and thus acceptance.