RN Braun observed that frequencies of health disorders in general practice are so consistent that he called his discovery "Case Distribution Law". Our study compares morbidity data from methodologically similar surveys in primary care practices over a period of fifty years. Frequency ranks were determined for each observation period and the first 150 ranks were compared with Spearman's correlation coefficients. All correlations were consistently positive. Frequency ranks were strikingly similar for surveys carried out at approximately the same time, especially when nomenclatural matching had been carried out before data collection. Ranks were also very similar where clear disease classifications were possible, but less so for non-specific symptoms.The consistency of the distribution of health disorders helps develop diagnostic strategies (diagnostic protocols) and appropriate labeling for non-specific, diagnostically open symptom classifications. According to Braun's considerations, the regularity of case distribution plays an important role in the professionalization of primary care.