Tail docking is still applied in Europe to prevent tail biting, despite its evident negative impact on pig welfare. We aimed at characterising consequences of tail docking on suckling piglets. We compared 48 piglets with tail docked (C) to 50 undocked piglets submitted to a non-painful simulation of docking (S). Their behavioural reaction during docking and for 20 s following the process was observed: vocalisations, tail posture and movements. Observations were repeated on C animals and on 48 other animals left intact from birth (I), 4 h after the docking process, 3 days after and once a week, in addition giving a score to the state of the tail. Fifteen days after birth, their reaction to a motionless seated human was observed. The C piglets vocalised more and louder during the docking process than S piglets (P < 0.05). For the 20 s after docking, their tail remained immobile longer (P < 0.05). The tail was also more immobile during the whole suckling period (P < 0.05). The C piglets approached the unfamiliar human later than the I piglets (P < 0.05). The I piglets tended to have more tail lesions than the C group (P < 0.1) during suckling. Tail docking thus induces reactions indicating pain on the day of docking and throughout the suckling period. Evidence of first episodes of tail biting were also found in I pigs. Longer term effects remain to be characterised (pain and bitings).