Objective: To explore incidence and prevalence rates of nutritional deficiency in adults in general practice. Methods: Six Dutch general practice research and registration networks supplied incidence and prevalence rates of nutritional deficiency by the International Classification of Primary Care (ICPC) or 'E-list' labels ('loss of appetite, feeding problem adult, iron, pernicious/folate deficiency anaemia, vitamin deficiencies and other nutritional disorders, weight loss'). In case of disease-related nutritional deficiency, we asked whether this was labelled separately ('co-registered') or included in the registration of the underlying disease. Results: 'Iron deficiency anaemia' had highest incidence (0.3-8.5/1000 person years), and prevalence rates (2.8-8.9/1000 person years). Nutritional deficiency was mostly documented in the elderly. In two networks 'co-registration, was additional, two only documented the underlying disease and two did not specify 'co-registration'. No clear difference was found between networks considering the difference in 'co-registration'. Conclusion: Nutritional deficiency is little documented in general practice, and generally is not registered separately from the underlying disease.