Tomato yellow leaf curl virus (TYLCV) and tomato yellow leaf curl Sardinia virus (TYLCSV) (genus Begomovirus, family Geminiviridae) as well as their whitefly vector Bemisia tabaci were reported from the south-west and central regions of Morocco. To establish a more comprehensive view of tomato begomoviruses and B. tabaci biotypes throughout Morocco, 32 tomato fields were surveyed for tomato yellow leaf curl disease (TYLCD) symptoms in southern and northern regions, and 54 samples of leaves from cultivated plants or weeds and 35 B. tabaci individuals were collected and analysed by PCR, randomly amplified polymorphic DNA and sequencing. Only TYLCV or TYLCSV were detected. TYLCV was detected in 15 plant samples whereas TYLCSV only in 4. Sequence analyses revealed the presence of the 'Spanish' strain of TYLCSV and distinguished two genetically distinct strains of TYLCV. The begomovirus infections were unevenly distributed throughout Morocco. In the north-west and north-central regions where tomato plants exhibiting TYLCD symptoms were rarely observed, only 1 sample out of 13 tested positive for the presence of a begomovirus. In the north-east region, the ratio of begomovirus-positive samples was higher, 6/13, and in the south-west region, it was the highest, 13/14. Consistently the frequency of plants exhibiting TYLCD-like symptoms in the northern regions was lower than that in the south-west region. B. tabaci biotype Q is present throughout the country and in Algeria, whereas biotype B, identified for the first time in Morocco, was detected only in the north-east region.