Background Non-malignant hematologic and immune disorders-related hospitalization trends are unstudied despite their importance from a public health standpoint. Therefore, this study aimed to define the hospitalization trends of the International Statistical Classification of Diseases-10 (ICD-10) category diseases of the blood and blood-forming organs and certain disorders involving the immune mechanism (B&ID). Methods We conducted an ecologic study to analyze hospital admission data obtained from England's Hospital Episode Statistics database and Wales' Patient Episode Database. Hospital admissions data for non-malignant hematologic disorders and immune disorders were extracted for the period from April 1999 to March 2019. We used the Poisson model to assess trends in hospital admissions. Results The total annual B&ID-related hospital admission (RHA) rate for all categories increased by 137.9% between 1999 and 2019 (p<0.01). Females accounted for 54% of all B&ID-RHA. Around 37% of B&ID-RHA were seen in the age group of 15-59 years and 29% in the age group of 75 years and above. The most common causes of B&ID-RHA were aplastic and other anemias and other bone marrow failure syndromes, ICD-10 category (33%) and nutritional anemias category (28%). Certain disorders involving the immune mechanism category accounted for the least number of B&ID-RHA (8.4%). The highest increase in B&ID-RHA was seen in the nutritional anemias category (3.86 fold), followed by certain disorders involving the immune mechanism (1.28 fold). Iron deficiency anemia accounted for 95.1% of all hospitalizations secondary to nutritional anemias. Around half of all, hemolytic anemia category hospitalizations were secondary to the sickle cell anemia subcategory. Conclusions Hospital admissions trends in non-malignant hematologic and immune disorders changed dynamically among age groups and gender in England and Wales over the last two decades. Understanding these changes has important implications for public health planning.