The morphology of sol–gel derived dip-coated yttria-doped zirconia ﬁlms containing variable amounts of yttria has been studied using in situ grazing-incidence small-angle X-ray scattering (GISAXS) whilst heated incrementally to 1000C. A procedure to analyse in situ GISAXS data has been devised which allows a quantitative analysis of time-dependent GISAXS data tracing processes such as chemical reactions or manufacturing procedures. To achieve this, the relative positions of the Yoneda peak and the through beam are used to ﬁx the vertical q scale when the sample thickness is subject to ﬂuctuations due to chemical reactions or deposition processes. A version of Beaucage’s uniﬁed model with a structure factor from Hosemann’s model for paracrystals describes the yttria-zirconia ﬁlm data best. It is interpreted in terms of particles forming from a polymeric gel network and subsequently agglomerating into larger units subject to Ostwald ripening as both size and average separation distance of the scattering objects increase. The sample with the highest yttria content shows progressive surface roughening from 850C which may indicate the onset of chemical segregation.