Thin films of YBa2Cu3O7-delta (YBCO) are deposited by laser ablation at substrate temperatures (T(s)) ranging from 575 to 850-degrees-C. The microstructure and growth behaviour of the films are found to be a sensitive function of T(s). We also find that the critical current density (J(c)) of the films is strongly related to the microstructure. It is proposed that the boundaries between a-axis and c-axis grains may act as pinning centres.