Background: Two lava flows from Nyiragongo volcano in January 18, 2002, made 120,000 people homeless and destroyed the fragile lifelines of Goma, a city on the shore of Lake Kivu located in eastern Democratic Republic of Congo in an area of humanitarian crisis. Methods: We made two field studies in Goma, in January and March 2002, to evaluate the health impact, including the cholera risk, a key factor in crisis management in Goma since the epidemic in refugee camps in 1994. Findings: Self-evacuation by most of the population was followed by re-occupation of Goma starting within two days and before the lava flows had cooled. Ground emissions of methane were associated with minor explosions, but there was little hazard of carbon dioxide from fissures. Apart from air pollution due to the fires ignited by the lava, air quality was unaffected, and fluoride levels in drinking water remained low. The destruction of housing resulted in overcrowding and 15,000 people relocated in camps, whilst the loss of lifelines placed pressure on the availability of food and fuel and the means for boiling or chlorinating water from the lake. Epidemiological surveillance found no major increases in infectious disease. Interpretation: Rapid response by relief agencies and local utilities workers prevented major epidemics, including cholera, but about 160 people died in the event. A future rifting eruption might trigger devastating lava-water explosions or a carbon dioxide/methane gas burst from Lake Kivu, which could lead to a greater loss of life than would arise from moving the population (c. 500,000) in a planned evacuation. Disaster planning and mitigation of these new risks will require resolution of the humanitarian crisis to be effective.