Detailed behavioural observations were made of broiler breeder chicks after their beaks had been trimmed by an automated infrared treatment at one day of age or by the traditional hot-blade method at one day or seven days, or after they had been sham-trimmed or left untreated. Observations took place immediately after the treatments and at regular intervals until six weeks of age; beak length and bodyweight were also measured regularly. There were no significant effects on the behaviour of the chicks in the first hour after trimming or in the subsequent six weeks. Variability in beak length was low within the treatments and there was significant regrowth, but it was least in the birds that had been hot-blade trimmed at seven days. Both beak-trimming methods were associated with small but significant reductions in bodyweight, with the hot-blade-treated birds being more affected.