Gelsolin is an actin-binding and an actin-fragmenting protein. It contains 730 amino-acids, organized in six G1-G6 homologous domains which determine different functions of the protein. Two variants of gelsolin, cytoplasmic and secreted (contained in plasma) are described. Cytoplasmic gelsolin re-organizes the structure of cytoskeleton and plays an important role as a capping protein. In addition, cytoplasmic gelsolin binds bacterial lipopolysaccharide and ATP and exhibits antibacterial and anti-inflammatory properties. Plasma gelsolin is synthesized mainly in skeletal and smooth muscles and myocardium. Plasma gelsolin was also found in: blood, lymph, bronchial epithelia, synovial fluids and cerebro-spinal fluid. The protein plays a role in the immune response, moreover it is involved in extracellular and blood actin-scavenger system. Plasma gelsolin has anti-amyloidogenic, anti-oxidant and anti-apoptotic properties and it has a potential for treatment of Alzheimer disease. Decreased levels of the gelsolin plasma isoform was observed in patients with sepsis, myocardial infarction, liver failure, acute respiratory distress syndrome, inflammations and after burns. On the other hand, after rhabdomyolysis and in amyloidosis gelsolin plasma level are increased. In this review we present recent data on the structure and functions of gelsolin and changes of its activity in some pathological processes.