The purpose of this study was to demonstrate the high incidence of atelectasis or pneumonia (A/P) in the left lung of acute spinal cord injured (SCI) patients. The study group consisted of 46 consecutive motor complete (Frankel A or B) SCI patients admitted within 48 hours of injury. The ages of the patients ranged from 15 to 72 years. Neurologic levels ranged from C3 to T11. There were 19 high-level quadriplegic patients (HLQ; C3-C5), 11 low-level quadriplegic patients (LLQ; C6-C8), and 16 paraplegic patients (Para; T1-T11). The patients were followed during the first 30 days postinjury for radiographic evidence of A/P lasting more than three days. The time of onset, duration, and location of A/P was determined. Fifty percent (23 of 46) of the patients developed A/P in the first 30 days after their spinal cord injury. The incidence was higher in the HLQ than in the LLQ and Para (74% vs 33%; p less than 0.02 using the Fischer exact test). There was a preponderance (4:1 ratio) of left-sided involvement for A/P in this population (p = 0.01 using the two-tailed binomial test). Sixteen patients had left-sided A/P, four patients had right-sided A/P, and three patients had bilateral findings. There was no relationship between level of injury and side of involvement. The high incidence of left-sided pulmonary involvement in the acute SCI patient may be due to the tendency to retain secretions in this period combined with the increased difficulty of clearing secretions from the left lung.