Phytoplasmas are plant endocellular parasites spread through the world. They range in size from 200 to 800 nm. Their genome is very small, from 530 kb to 1350 kb. Phytoplasmas lack a number of genes involved in: (I) essential metabolic pathways, like F0F1-type ATP–synthase and pentose phosphate pathway, (II) biosynthesis of amino and fatty acids, (III) metabolism of amino acids, nucleotides, sugars, glyoxylate and (IV) CO2 fixation. In plants they reside in sieve elements and move around through the sieve pores, where plant’s sap provides nutrients. To this date, few ‘Ca. Phytoplasma species’ have been detected in gymnosperms - ‘Ca. P. pini’, X disease phytoplasma from 16S rIII group, ‘Ca. P. trifolii’ and ‘Ca. P. phoenicum’. In Croatia, ‘Ca. P. pini’ is detected in two pine species Pinus mugo and P. halepensis. Infected plants exhibit number of symptoms which include shoot proliferation (whiches’ broom), stunting, leaf yellowing, phyllody and dwarfing. Due to phytoplasma infection economic losses in the production of many plant species are substantial. So far, impact and possible consequences of phytoplasma infection in conifers are not known. However, scientists do warn that phytoplasma presence in conifers might present a threat to timber industry. It is thought that phytoplasma infection causes trees to be more vulnerable to infection with fungi and/or other damaging abiotic factors.