Simulations of Langmuir circulation with constant eddy viscosity that reveal considerable levels of spatial and temporal complexity are reported. In field observations, the simulations could be interpreted as evidence of vacillation in space and time of measured features in the circulation system, and of the presence of defect structures in the windrow patterns in which the local spacing changes by a factor of 2 in a distance short compared to the windrow spacing. The results also suggest that the ratio of downwind jet speed to downwelling speeds (pitch) can be highly variable and is not a robust feature of Langmuir circulations. ¿ American Geophysical Union 1995