In January 1998 encoding of the diagnoses of all inpatient will change from ICD-9 to ICD-10. This necessitates the conversion of ICD-9 codes to ICD-10 codes and vice versa for different purposes. We present a first version of conversion tables between ICD-9 and ICD-10 for interactive use by physicians. The basic method to construct these tables was a modified vector space text retrieval method using word stems. Stemming was done by a lexicon based method on all available textes for ICD-9 and ICD-10. The first output was an automatic generated list of weighted mappings which was filled up by published mappings. Finally the list was revised manually. Doing this took us three months to generate the presented tables. The main results are: direct mapping from ICD-9 to ICD-10 can be done in 65%, from ICD-10 to ICD-9 in 85%. The next version of the tables will have an improved quality, a higher rate of direct mappings from ICD-10 to ICD-9 and more marked automatic mappings and will be released at the end of 1996. Then it should be possible to convert ICD-10 codes automatically into ICD-9 codes. It seems impossible to map from ICD-9 to ICD-10 automatically. The presented vector space text retrieval method is also very helpful to encode complete diagnosis or treatment phrases e.g. direct out of the discharge summary into a corresponding classification.