Platelet δ-storage pool disease (δ-SPD) is a platelet function disorder characterized by a reduction in the number or content of dense granules. Reports on δ-SPD are mostly limited to case presentations. We aimed to retrospectively describe a series of patients with δ-SPD to better characterize the disease. We studied 16 patients with congenital or acquired δ-SPD. Lumiaggregometry, α- and δ-granules content, platelet ultrastructure, αIIbβ3 integrin, and glycoprotein Ib (GPIb) activation were assessed. Most of the patients generally demonstrate mild to moderate bleeding diathesis. Platelet aggregation studies showed moderate abnormalities with variable profiles, while all the individuals had almost complete absence of adenosine triphosphate release. Mepacrine capture, CD63 expression, and study of dense granules by electron microscopy enabled to distinguish different subtypes of δ-SPD with quantitative or qualitative defect. Surprisingly, significantly decreased GPIb expression levels after platelet activation with thrombin receptor activating peptide 50 μM were found, suggesting that GPIb-impaired mobilization may represent an additional feature of the disorder. In conclusion, δ-SPD represents a complex disorder with various clinical and biological aspects, requiring a great deal of expertise to be properly diagnosed.Read less <