Inspiratory strength after a neck dissection has not been evaluated, and diaphragm function has not been adequately evaluated. Evaluate diaphragm mobility and inspiratory strength after neck dissection. Prospective data collection of a consecutive series of adult patients submitted to neck dissection for head and neck cancer treatment, in a tertiary referral cancer center, from January to September 2014, with 30days of follow-up. A total of 43 were studied (recruited 56; excluded 13). Determine diaphragm mobility and inspiratory muscle strength after neck dissection, using diaphragm ultrasound and by measuring maximal inspiratory pressure (MIP) and sniff nasal inspiratory pressure (SNIP). Thirty patients underwent unilateral neck dissection, and thirteen patients underwent bilateral neck dissection. Diaphragm immobility occurred in 8.9% of diaphragms at risk. For the entire cohort, inspiratory strength decreased immediately after the dissection but returned to preoperative values after 1month. Except for those with diaphragm immobility, diaphragm mobility remained unchanged after the dissection. One month after the dissection, the diaphragm thickness decreased, indicating diaphragm atrophy. Immediately after a neck dissection, just a few patients showed diaphragmatic immobility, and there was a transient decrease in inspiratory strength in all individuals. Such findings can increase the risk of postoperative complications in patients with previous lung disease.