Crystal-induced inflammatory process may mimic symptoms of many diseases connected with other aetiopathological factors. The most common example is pseudogout caused by CPPD crystals and pseudoosteoarthritis in patients with chondrocalcinosis. Tophaceous gouty arthritis mimicking rheumatoid arthritis and rheumatic features masking hyperlipoproteinaemia are also described. Very important diagnostic tools in patients with crystal--included diseases are: synovial fluid analysis, biopsy of tissues with deposit of crystals and imaging.