We have measured the time evolution of the self-assembly process in perpendicular-oriented cylindrical-phase diblock copolymer thin films using statistical analysis of high-resolution scanning electron microscope (SEM) images. Within minutes of annealing above the polymer glass-transition temperature, microphase separation between polymer blocks results in formation of uniform nanometer-scale domains whose relative position is initially largely uncorrelated. On further annealing, the cylindrical polymer domains organize into a two-dimensional hexagonal lattice whose characteristic grain size increases slowly with time (similar tot(1/4)). (C) 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1970-1975, 2004.