[en] Lithuania is a relatively small country with the population of 3,5 mln, disproportionately powerful energy industry and low energy consumption. Installed electricity generating capacities are more than 6 GW, but total power demand is less than 2 GW. Lithuania with average electricity consumption about 2900 kWh per person occupies one of the last places in Europe. Nuclear is the main source of electric energy in Lithuania: it covers 60 - 86% of total electricity production. Comparing consumption of all primary energy sources in all branches of economy nuclear covers about one third (32 - 37%) of the whole alongside with oil (31 - 33%) and natural gas (30 - 31%). At Ignalina NPP Lithuania are operating two the RBMK-1500 type reactors - the most advanced version of the former Soviet Union channel type reactor design series. The designed electrical power of RBMK-1500 reactor (1500 MW) is the biggest in the world for the single unit. The first unit of INPP was put into operation by the end of 1983 and the second unit in 1987. After Chernobyl accident the maximal allowed electrical power of each reactor at INPP was reduced to 1350 MW. The initial RBMK-1500 design at Ignalina NPP at the present time is substantially improved. More than 200 million US dollars of western countries support were spent, and numerous safety features were implemented. Nowadays both Lithuanian and foreign experts agree, that the safety level of Ignalina NPP is very similar to the western type NPP's of the same age. During accession process, one of the main EU requirements to energy sector of Lithuania was to close both reactors of Ignalina NPP, which were decided to be unsafe in principle. Despite all efforts of Lithuanian specialists and negotiators shutdown of the 1st reactor of INPP is foreseen at the end of 2004 and shutdown of the 2nd reactor is foreseen at the end of 2009. Closure of Ignalina NPP will decrease maximal power generating capacity to 2641 MW in 2010 and will cause a complex of serious economical, ecological, and social problems. Trying to evaluate these problems, an attempt was made to foresee trends of further economy development and energy demand for next 20 years. The econometric models, comparative analysis and analytical expertise evaluation methods were used. Three different scenarios of future energy consumption growth were analysed. Results of the performed analysis show, that in the year 2020 energy demand should be about 15,3 - 22,1Twh in cases of the slow or very fast growth scenario (3197 MW and 4484 MW respectively, taking into account necessary reserves). This leads to a shortage of Lithuania's power generating capacity already by 2010. In 2020 this shortage can increase to 556 MW in case of the slow growth scenario and 1843 MW in case of the very fast growth scenario. Three possible ways to compensate this shortage increasing the share of power plants using fossil fuel, broadening the exploitation of renewable energy resources, and nuclear option are analysed. Both economical and ecological problems, including the price dynamics of main imported energy resources, especially of oil and natural gas, are taken into account. It is pointed out that according to Energy Strategy of Russia average contract price of gas can reach 119 - 138 USD/10³ m³ in 2020 (growth of price 138 - 160% compared to 86 USD/10³ m³ in the year 2000). The unreliability of fuel supply from single supplier (Russia) is emphasized. Analysis and assessment of positive and negative aspects of different energy generation means shows that perhaps the best solution in perspective for Lithuania is the nuclear option. It can be realised by following means: a) extension of exploitation of the second unit of Ignalina NPP after the year 2010, b) replacement of existing RBMK-1500 reactors by modern BWR or PWR reactors, using existing turbines and infrastructure, and c) construction of new nuclear power unit or plant. Results of this study illustrate, that all nuclear scenarios listed above are not only competitive but also have evident advantages over energy production based on burning fossil fuels.(author)