The significant limits within which crustal movement can be determined by geodetic survey methods depend on the quality of the observations, the stability of the markers in the network, and the structure of the network. The paper presents a study of vertical movement in the Lac St. Jean area of Québec. The data used covers the periods 1919–1938 and 1962–1966. With reference to a line of levels from Ste. Anne de la Pérade to La Malbaie along the north shore of the St. Lawrence River, the results show annual uplift as high as 10 mm at Seneterre and subsidence amounting to 4 mm at Stoneham, north of Quebec City. Confidence intervals, at the 95% level, for rates of movement are given as indicators of the quality of the results.