Inclusion Criteria:

- Folicular Lymphoma CD20-positive, grade 1, 2 or 3a, confirmed in previous 4 months.

- Patients no treated previously.

- Ann Arbor Stage II, III o IV.

- Symptoms or signes wich indicate necesary treatment (GELF criteria):

- Ganglionar or extraganglionar mass

- B Symptoms

- LDH or B2-microglobuline increased

- 3 ganglionar territory afected (> 3 cm)

- Esplenomegalia

- Compresive syndrome

- Pleural/peritoneal effusion

- Secondary medular insufiency due to infiltration

- Age> 18 years and <75 years.

- ECOG < 2

- Adecuate hematological function: Hemoglobin > 8,0 g/dl (5,0 mmol/L); RAN >1,5 x
109/L; platelets > 100 x 109/L

- No pregnant women. Women and man should use an appropiate anticonceptive method
during the study and one year after

- Informed consent

Exclusion Criteria:

- Transformation in high grade lymphoma

- FL grade 3b.

- Skin or gastro-intestinal primary lymphoma

- History of CNS diseases ( or CNS lymphoma)

- Previous treatment

- Regulary treatment with corticosteroids (permited < 20 mg/day prednisone or
equivalent).

- Previous cancer diseases

- Major surgery in 28 days before inclusion in study.

- Creatinine > 2,0 mg/dl (197 mmol/L)

- Bilirubin > 2,0 mg/dl (34 mmol/L), AST (SGOT) > 3 x upper normal limit.

- HIV infection or active infection VHB o VHC < 4 weeks before inclusion.

- Other complicated diseases

Criteria investigador:

- Life expectancy < 6 months.

- Hipersensibility to Ibritumomab tiuxetan, rituximab, other murines proteins or any
excipients.

- Treatment in other experimental study in previous 30 days

- Any medical o psicologycal condition that can modify the capacity to give the consent