The deployment of wireless local area networks (WLANs) has recently gained in popularity with roll-out densities often reaching saturation levels. The frequency bands designated to WLANs do thus not suffice anymore to provide non-overlapping, and hence interference-free, communication. Prior research has therefore been dedicated to a wide variety of mainly cochannel interference mitigation techniques. Our contribution lies in the performance analysis of the more realistic case of spatially close WLAN systems interfering asynchronously in DSSS mode and on adjacent channels. The authors expose the performance of optimum and sub-optimum multiuser detection maximum likelihood sequence estimators (MUD-MLSEs) under varying conditions, e.g. level of interference, degree of spectral overlap, etc. This facilitates a better understanding and design of future interference-limited WLAN systems. The performance results are also important to spectrum policy makers, allowing to knowledgeably estimate the degree of tolerated interference in license exempt bands.