The complexity of some complex sentence types in Urban Moroccan Arabic is studied here and compared with some other dialects of Arabic The types relative, direct object, subject and (nominal) predicate clauses, and all expansions of NP, and seem to be related both in structure and use (or deletion of subordinating conjunctions. The variety of sub-classes that exists for the four types, as as their conditioning, may indicate the complexity involved. Some processes of distinction between structures seem to be developing still, and it is interesting to compare them with earlier stages of Arabic ( Classical and Middle Arabic).