The causative agent of cotton leaf curl disease has previously been shown to be transmissible by the whitefly Bemisia tabaci (Gennadius) and a begomovirus (Geminiviridae) was shown to be associated with the disease. This virus was provisionally called cotton leaf curl virus (CLCuV) although no causal relationship between virus and disease was shown. In the present study full-length clones of CLCuV, equivalent to the DNA A component of bipartite begomoviruses, were obtained. The clones of CLCuV were systemically infectious to both Nicotiana benthamiana and cotton. Infected plants did not exhibit symptoms characteristic of cotton leaf curl disease, producing mild leaf curling, yellowing and some stunting. Efforts to identify a second genomic component were not successful. These findings suggest that the begomovirus, CLCuV, is not or not the sole cause of cotton leaf curl disease. The transmission of cotton leaf curl disease by B. tabaci, however, may indicate that the begomovirus plays a part in the transmission of the disease. The implications of these findings are discussed.