We studied spatial variation of the body weight in adult capercaillie (Tetrao urogallus) using materials compilated from the literature, mostly for Western Europe. The data on > 4,300 males and > 1,000 females were grouped, respectively, into 45 and 29 mean population estimates; the principles of rejection, correction and grouping of initial data are presented. High values of male weight (≥ 4.2 kg) were located within the strip of land running from eastern France to western Belarus and northern Ukraine, which covered the range of T. u. major. To the north and south of this strip, their weight showed a clinal decrease with minimal values in the north (Swedish and Finnish Lapland: 3.7-3.8 kg) and southwest (Cantabria, Pyrenees: 3.3-3.4 kg). Such a disposition supports the opinion about a discrepancy between prediction by Bergman' rule and observed variation in the weight of West European capercaillie. However, weight in southern populations (Cantabria, Pyrenees, Eastern and Southern Carpathians, Rhodopes) increases from west to east in accordance with this rule, confirming the opinion on its correctness for monophyletic taxa. In general, the weight of females follows the variation pattern of males, although the reliability of estimates for females is substantially lower, mainly due to smaller samples. For the entire region on average, the weight of females reaches ~ 47.5 % of the weight of males, which is consistent with previously reported estimates. Possible causes for distortions of mean population weight values are discussed.