We describe the process of putting into practice a computer-based clinical decision support (eCDS) service integrated in the electronic patient record, and the actual use of eCDS after one year in a primary care organization with 48 health care professionals. Multiple methods were used to support the implementation. The actual use was measured by means of a questionnaire and statistical data. The implementation process consisted of three successive training rounds and lasted for 18 months. After 12 months the reported actual use of the eCDS functions was diverse. The study indicates that successful implementation of eCDS requires time and repeated supportive input. Primary care professionals need time and training for adapting eCDS in their daily routine. In addition, the eCDS content should be tailored to fulfil different professionals’ information needs in primary care practice.