Health conditions are associated with a variety of functional outcomes. Even though functional outcomes are diverse for different health conditions, they can have important commonalities. The aim of this study was to identify the most common problems in functioning across the wide range of health conditions using the International Classification of Functioning (ICF). Existing databases created for the 21 ICF Core Sets studies were descriptively analyzed. These included data collected in 44 countries on 9978 patients with one of 21 health conditions as the main diagnosis. A frequency cutoff of 50% was used to identify the most common problems in functioning when looking at single health conditions and across them. No category was identified as common to all health conditions included in the study. Fifteen most frequent categories were common in 10 to 13 health conditions out of 21. Eleven categories correspond to the list of activities and participation, and four to the list of body functions. These are related to mobility, daily routine, mental functions, intimate relations, employment, and leisure. Some health conditions have more commonalities between each other. The most common problems across health conditions are therefore related to mental functions, mobility, daily life, intimate relations, employment, and leisure. The results contribute toward the identification of the universal set of ICF categories that can be used in clinical practice for the general assessment of functioning.