Background: Inpatient healthcare demand is influenced by demographic changes; however, existing research mainly focuses on age-related conditions among older age groups and lacks empirical evidence. We aimed to identify important indicator diagnoses by group, which best characterise age-specific conditions and their demand of inpatient services in Germany. Methods: Data stem from the general hospital diagnosis-related group (DRG) statistics in Germany from 2005 to 2010. To identify the indicator diagnosis groups, we used frequency analyses of individual diagnoses and combined them into common diagnosis groups, stratified by age and gender. We identified indicator diagnoses by the highest number of cases of inpatient hospital treatments in 2010 or the largest change in cases between 2005 and 2010. The most common diagnosis groups were then ranked using different weights. Changes were quantified using linear regression. Results: Across all ages, 13 diagnosis groups were identified as frequently reported hospitalisations such as injuries to the head (S00-S09) among patients aged 0 to 17 years, and ischemic heart diseases (I20-I25) among patients aged 18 to 64 years. As the number of hospitals decreased, the demand in inpatient services increased. From 75 years and above, males were more frequently inpatients than females, and overall length of stay in hospitals appeared to decrease. Conclusion: We empirically identified 13 diagnosis groups, which best describe the inpatient services utilised among various age groups in a ranked order. Findings from this study can provide a platform for determining future demand of inpatient services as well as the demographic-specific diagnoses that need attention.