During the recent years, power industries have been facing significant changes due to deregulation and liberalization of the energy markets and increase of the installed capacity of renewable energy sources. These factors directly affect the transmission network planning (TNP) task and inspire a search for new, more adequate methods. This paper compares a deterministic method — the economic intervals (EI) method — and the stochastic approach based (SAB) method. Both methods are used for designing the overhead power line (OHPL), choosing the optimum conductor type and cross-section as well as other main line parameters such as the height, type and coordinates of towers, the line route, the line fittings, etc. Moreover, the paper presents a new approach for implementing a stochastic optimization procedure with a statistical representation of the electricity prices, ambient temperature and load currents in the transmission network. The problem is formulated as minimization of the total annual costs for the transmission line (TL) construction project. The tool is implemented in MATLAB software by using the Monte Carlo (MC) method as well as in OHPL designing software — PLS-CADD.