Summary Background Recent evidence suggests that embryonated eggs of the porcine whipworm Trichuris suis ova (TSO) may be an effective treatment for inflammatory bowel disease (IBD). Aim To assess the safety and tolerability of TSO following a single dose in patients with Crohn's disease. Methods This was a sequential dose‐escalation (500, 2500 and 7500 viable embryonated TSO), randomised, double‐blind, placebo‐controlled study to evaluate the safety of a single dose of oral suspension TSO in patients with Crohn's disease. Twelve patients were randomised into each of three cohorts. Patients were assessed 1, 3, 5, 7, 9, 11 and 14 days following dosing (via a telephone call and diary symptom collection through 14 days postdose) for adverse events, changes to concomitant medications and gastrointestinal (GI) signs and symptoms. Patients were again assessed at Months 1, 2 and 6. Results Eighteen males and 18 females were enrolled, ages 20 to 54 years. All patients were dosed and completed the initial 2‐month follow‐up period (five patients did not attend their 6‐month study visit). GI disorders were reported with the highest frequency; 7 (25.9%) TSO‐treated patients and 3 (33.3%) placebo‐treated patients. No dose‐dependent relationship was observed, with 3 (33.3%) placebo, 4 (44.4%) TSO 500, 0 (0.0%) TSO 2500 and 3 (33.3%) TSO 7500 patients experiencing at least one GI event, and no clinically meaningful changes in GI signs and symptoms. Conclusions A single dose of Trichuris suis ova up to 7500 ova was well tolerated and did not result in short‐ or long‐term treatment‐related side effects. Clinicaltrials.gov NCT01576461.