Carbamazepine (CBZ) is well known to typically present as needles for CBZ form II and as blocks for CBZ form III. However, in spite of only detecting CBZ III in the in situ Powder X-ray Diffraction data after post-nucleation seeding, aggregated needles were the main habit observed, in addition to a low proportion of small blocks. This is an unusual case of crystallising CBZ form III needles. The two habits are shown to separate as a result of their different interaction with the flow paths.